System and method of monitoring contamination

ABSTRACT

The present invention provides passive sampling systems and methods for monitoring contaminants in a semiconductor processing system. In one embodiment, that passive sampling system comprises a collection device in fluid communication with a sample line that provides a flow of gas from a semiconductor processing system. The collection device is configured to sample by diffusion one or more contaminants in the flow of gas.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 10/662,892 filed Sep. 15, 2003, which is acontinuation-in-part of U.S. patent application Ser. No. 10/395,834filed Mar. 24, 2003, which is continuation-in-part of U.S. patentapplication Ser. No. 10/253,401 filed Sep. 24, 2002, now U.S. Pat. No.6,759,254, which is a continuation-in-part of U.S. patent applicationSer. No. 09/961,802, filed Sep. 24, 2001, now U.S. Pat. No. 6,620,630.The entire contents of the above patents and applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Semiconductor manufacturers continue to measure and control the level ofcontamination in the processing environment, especially during thecritical steps of the photolithography processes. The typical means ofdetermining the quality and quantity of contamination in gas samples incleanroom manufacturing environments involves sampling air and purgegases, such as, for example, filtered and unfiltered air, clean dry air,and nitrogen, with sampling tubes or traps, typically containingadsorptive medium such as, the polymer Tenax® This sampling process isfollowed by analysis using thermal desorption, gas chromatography andmass spectrometry (TD/GC/MS). The combination of TD/GC/MS providesidentification of sample components and a determination of theconcentration of these components. The most abundant contaminants inthese manufacturing environments are low molecular weight componentssuch as acetone and-isopropyl alcohol. The current sampling time forexisting traps typically varies between 0.5 and 6 hours with totalaccumulated sample volumes ranging typically between 20 and 50 liters.

Further, in applications that are directed to the manufacturing of oruse of optical elements such as, for example, photolithography, thedetection and quantification of compounds having a higher molecularweight such as, for example, siloxanes is of primary concern. Thesecompounds having a higher molecular weight are, however, typically inmuch lower concentrations as compared with the low molecular weightspecies. Further, the compounds having a high molecular weight can alsobe defined as condensable compounds with a boiling point typicallygreater than approximately 150 degrees C. The current methods fordetermining contamination have the limitation of the sample volume beingbased on the total trap capacity of the lighter or lower molecularweight components, for example, compounds having typically less than sixcarbon atoms. As the heavier components are usually present at muchlower concentrations, the collection of a significant mass of thesehigher molecular weight species is limited.

In addition, polluting or contaminating substances may adhere onto theoptical elements and reduce the transmission of light. Currentlyairborne contamination is addressed in cleanroom environments withlittle regard for contaminants that may be adsorbed onto the surfaces ofoptical elements. The adsorbed contamination reduces the transmission oflight through the optical elements and system.

Thus, contamination of optical systems is emerging as a significant riskto photolithography and other semiconductor manufacturing processes asshorter wavelengths of the electromagnetic spectrum are exploited.However, molecular films on optical surfaces physically absorb andscatter incoming light. Scattered or absorbed light in photolithographyoptical surfaces causes distortion of the spherical quality ofwavefronts. When the information contained in the spherical wavefront isdistorted, the resulting image is also misformed or abberated. Imagedistortions, or in the case of photolithography, the inability toaccurately reproduce the circuit pattern on the reticle, cause a loss ofcritical dimension control and process yield.

Typically, filter systems are used to remove molecular contamination insemiconductor processing environments. Systems are in place to measurethe performance of such filter systems. However, typical monitoring offilter performance includes measurement of filter breakthrough either byprocess failure or by detection of the target filtered gas at thedischarge of the filter system. However, these measurement means detectbreakthrough after it has occurred.

A need still exists for determining, accurately and efficiently, thepresence and quantity of contaminants that can alter and degrade theoptical systems in semiconductor processing instruments. There furtherremains a need to monitor the performance of gas phase filter systemsprior to a breakthrough failure.

SUMMARY OF THE INVENTION

The preferred embodiments of the system of the present invention providean accurate and efficient system of determining and/or controlling thequality and/or quantity of contamination within a gas sample which canreduce the performance of optical elements used in semiconductorprocessing instruments, such as, for example, within the light path of adeep ultraviolet photolithography exposure tool. In a preferredembodiment of the present invention, the contamination may be gaseous aswell as contamination adsorbed onto optical surfaces. Opticalperformance can be evaluated without limitation as the level oftransmitted or reflected light through an optical system. Theembodiments of the system and method of the present invention arepredicated on the recognition that compounds having both high and lowmolecular weights can contribute to the contamination of optical systemsbut can operate at different rates. As such, the contaminants thatnegatively impact the performance of optical elements can be describedin terms of different orders, such as, for example, first, second andthird order effects.

First and second order contaminating effects have a greater impact oncontamination of optical systems than third or fourth ordercontaminants. The first order contaminants may comprise high molecularweight organics such as, for example, C₆ siloxanes and C₆ iodates withan inorganic component which is not volatilized through combination withoxygen. Second order contaminants may comprise high molecular weightorganics, such as, for example, compounds including carbon atoms withinthe range of approximately six to thirty carbon atoms (C₆-C₃₀). Thirdorder effects can arise due to the contaminating effects of organicssuch as C₃-C₆ that have approximately three to six carbon atoms. Fourthorder contaminants include organics such as, for example, methane, thathave approximately one to five carbon atoms. In many applications, thefirst and second order contamination can have a much lower concentrationthan the third and/or fourth order contamination, yet have asignificantly greater effect on the operation of the system.

A preferred embodiment in accordance with the present invention of amethod for detecting and monitoring, and preferably removingcontamination in a semiconductor processing system includes delivering agas sample from the processing system to a collection device. The methodfurther includes collecting contamination which comprises refractorycompounds, and high and low molecular weight compounds, from the gas inthe collection device by sampling the gas for a duration exceeding thesaturation capacity of the collection device for high molecular weightcompounds. The compounds having a high molecular weight are condensablewith a boiling point typically greater than approximately 150 degrees C.

A preferred embodiment of the system and method of the present inventionfor determining contamination includes the detection of refractorycompounds such as, for example, siloxanes, silanes and iodates, and highmolecular weight organics. The preferred embodiment includes the removalof refractory compounds, high molecular weight organics and lowmolecular weight organics, all of which contribute to the contaminationof optical systems, but which can operate at different contaminationrates.

The system of the present invention for determining contamination canuse different types of sample collecting media. In a preferredembodiment, the sample collecting media can emulate the environment ofthe optical surfaces of interest such as, for example, the absorptive orreactive properties of the optical surfaces. A measure of contaminationadsorbed onto optical surfaces enables the minimization and preferablythe removal of the contaminants. In another preferred embodiment, apolymer that has a high capacity for absorbing the compounds with a highboiling point is used in a collection device such as, for example,Tenax® a polymer based on 2-6 diphenyl p-phenylene. The operation of thesystem in accordance with a preferred embodiment of the presentinvention includes quantitatively measuring the concentration of bothlow and high boiling point compounds in the same sample wherein thecollection device has been driven beyond the breakthrough volume orsaturation capacity of the collection media to capture the low molecularweight compounds. The breakthrough volume of the collection device isdefined in a preferred embodiment as the quantity of gas needed to gobeyond the adsorption capacity of the device.

In accordance with a preferred embodiment of the present invention, themethod for detecting contamination includes a sampling time extended by,for example, a number of hours, days or weeks to enable collection of anappropriate mass of contaminants which are present in relatively lowconcentration. In a preferred embodiment, the sampling time is typicallybeyond the breakthrough capacity of the collection device for lowmolecular weight components, is at least six hours long and preferablywithin a range of six to twenty-four hours for a sampling tube system.The extended time allows for the collection of higher masses ofrefractory compounds and higher molecular weight compounds that mayinterfere with the performance of optical components even more than lowmolecular weight compounds. The higher molecular weight compoundsinclude, but are not limited to, for example, siloxanes and silanes.

In accordance with another preferred embodiment of the presentinvention, a semiconductor processing instrument, for example, aphotolithography cluster, includes a filtering system to removecontaminants. The filtering system includes a selective membrane tofilter organic compounds from a gas stream.

A preferred embodiment includes a method for monitoring the performanceof a filter positioned in an airstream in a semiconductor processingsystem. The method includes sampling the airstream at a locationupstream of the filter to detect the molecular contaminants present inthe airstream, identifying a target species in the contaminants upstreamof the filter, selecting a non-polluting species of a contaminant havinga concentration greater than a concentration of the target species,measuring the non-polluting species in the airstream at a plurality oflocations, and determining the performance of the filter with respect tothe target species from measurements of the non-polluting species. Theplurality of locations includes, but is not limited to, a locationdownstream of the filter and at a location within the filter. Further,the method for monitoring includes generating a numerical representationof a chromatogram of the airstream sampled at a location upstream of thefilter. The method for monitoring includes the non-polluting specieshaving a molecular weight that is lower than that of the target species.A correlation is established between the low and high molecular weightcompounds. In addition, in the method for monitoring, the step ofsampling includes collecting refractory compounds, high molecular weightcompounds and low molecular weight compounds. The filter comprisesabsorptive material.

A preferred embodiment includes a system for determining and monitoringcontamination in a photolithography instrument, having at least onecollection device in fluid communication with a gas flow extendingthrough an optical system of the tool, the collection device having amaterial analogous to optical elements, and a light source providinghigh energy light to the collection device such that at least onecontaminant in the gas flow reacts with the light to create a depositionlayer on the material. Further, the system includes at least onephotodetector coupled to the collection device to detect the presence ofthe deposition layer on the material by monitoring either the spectralor transmission differences. The material in the system comprises glassspheres having predetermined surface properties for adsorption ofcontaminants. The material is at least one of glass and coated glassmaterial. The contamination includes at least one of refractorycompounds, high molecular weight compounds and low molecular weightcompounds.

In accordance with another aspect of the present invention, an apparatusfor determining contamination in a semiconductor processing systemincludes a filter system having a plurality of filter traps forcollecting contaminants from a gas stream for a duration, and aninterface module coupled to the filter system in fluid communicationwith a gas flow extending through the processing system and directing aportion of the gas flow into and out of the filter system.

The contaminants include at least one of refractory compounds, highmolecular weight compounds and low molecular weight compounds. A vacuumsource can be coupled to the filter system to increase a pressuregradient across the filter traps. The filter traps can have a permeablemembrane that filter contaminants such as at least one of a refractorycompound, a high molecular weight compound and a low molecular weightcompound from the gas flow.

In preferred embodiments, the interface module further comprises apressure regulation device, a controller, electronically controlledvalves to impose a duty cycle for sampling, a timer device to determinea sampling duration and a cooling device such as a thermoelectriccooling device. Further, the filter traps have an absorptive materialsuch as a polymer, for example, Tenax®.

The foregoing and other features and advantages of the system and methodfor determining and controlling contamination will be apparent from thefollowing more particular description of preferred embodiments of thesystem and method as illustrated in the accompanying drawings in whichlike reference characters refer to the same parts throughout thedifferent views. The drawings are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described withreference to the following drawings, wherein:

FIG. 1 is a graphical representation of contamination coefficient versusmolecular weight;

FIG. 2 is a graphical representation illustrating a comparison of apreferred embodiment of the system for determining contamination withrespect to sample mass in a trap and sampling time in accordance withthe present invention and the prior art;

FIG. 3 is a graphical representation illustrating analyzed spectralcomparisons of the system and method of determining contamination inaccordance with a preferred embodiment of the present invention and theprior art;

FIG. 4 is a graphical representation illustrating surface coverage as afunction of contamination level in accordance with a preferredembodiment of the present invention;

FIG. 5 is a preferred embodiment of a system of determiningcontamination in accordance with the present invention;

FIG. 6 is a preferred embodiment of a refractory trap system inaccordance with the present invention;

FIG. 7 shows a flow chart of a method of detecting contamination inaccordance with a preferred embodiment of the present invention;

FIG. 8 is a diagram illustrating a preferred embodiment of a filteringsystem in accordance with the present invention;

FIGS. 9A and 9B illustrate a schematic block diagram of a filter devicehaving a bed showing the retention of different species in the bed and agraphical representation of the efficiency of the filter bed withrespect to time by measuring the different species, respectively, inaccordance with a preferred embodiment of the present invention;

FIG. 10 is a flowchart of a method for monitoring the performance of agas phase filter system in accordance with a preferred embodiment of thepresent invention;

FIG. 11 is a schematic diagram of a system that includes a filter systemin accordance with a preferred embodiment of the present invention;

FIGS. 12A-12C are graphical illustrations of chromatograms of a gassample including an average ion scan of the spectra end (FIG. 12C) inaccordance with a preferred embodiment of the present invention;

FIGS. 13A and 13B are chromatograms of a second gas sample in accordancewith a preferred embodiment of the present invention;

FIG. 14 is a graphical illustration of a chromatogram of a sample of oilfree air sampled at a location prior to a filter in accordance with apreferred embodiment of the present invention;

FIG. 15 is a graphical illustration of a chromatogram of a sample of oilfree air sampled at a location after the filter in accordance with apreferred embodiment of the present invention;

FIG. 16 is a graphical illustration of a chromatogram of a sample ofnitrogen gas sampled at a location prior to a filter bed in accordancewith a preferred embodiment of the present invention;

FIGS. 17A and 17B graphically illustrate a chromatogram of a sample ofnitrogen gas sampled after the filter system and an average ion scan ofthe end of the spectra, respectively, in accordance with a preferredembodiment of the present invention;

FIG. 18 graphically illustrates a chromatogram of a empty sampling tubein accordance with a preferred embodiment of the present invention;

FIG. 19 is a flow chart of a method for on-line, real-time monitoring ofthe performance of a filter system in accordance with a preferredembodiment of the present invention;

FIG. 20 illustrates a schematic block diagram of a system using a systemfor determining and monitoring contaminants and performance of a filtersystem in accordance with a preferred embodiment of the presentinvention;

FIG. 21 illustrates a schematic diagram of system modules in accordancewith a preferred embodiment of the system for determining and monitoringcontaminants and the performance of a filter system of the presentinvention;

FIG. 22 illustrates a schematic diagram of a module having a pluralityof filter traps of the system shown in FIG. 20 in accordance with apreferred embodiment of the present invention;

FIG. 23 illustrates an alternate view of the module having a pluralityof filter traps as shown in FIG. 21;

FIG. 24 illustrates a detailed view of the module having a plurality offilter traps as shown in FIG. 21 along with the plumbing in themanifolds in accordance with a preferred embodiment of the presentinvention;

FIGS. 25A-25C illustrate schematic diagrams of a device that functionsas a concentrator in a filter system in accordance with a preferredembodiment of the present invention;

FIGS. 26A and 26B illustrate schematic block diagrams of a detectionsystem that emulates and detects a deposition process on opticalelements in accordance with a preferred embodiment of the presentinvention;

FIG. 27 is a schematic illustration of a passive sampling system inaccordance with various embodiments of the present invention;

FIG. 28 is a flow chart of methods for passive monitoring ofcontaminants in a semiconductor processing system in accordance withvarious embodiments of the present invention;

FIGS. 29A-29B are schematic diagrams illustrating one embodiment of asystem for detecting airstream backflow in a semiconductor processingsystem in accordance with a preferred embodiment of the presentinvention;

FIGS. 30A-30E illustrate schematic diagrams of a device that functionsas a concentrator in a filter system in accordance with a preferredembodiment of the present invention; and

FIGS. 31A-31E illustrate a schematic diagram of a system using a devicefor monitoring contaminants and performance of a filter system inaccordance with a various embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a system and method for determiningand controlling contamination. Preferred embodiments of the presentinvention address gaseous contamination as well as the contaminantsadsorbed on surfaces, for example, an optical surface. The latter ismore critical to the performance of the optical elements.

Table 1 illustrates various species in a cleanroom environment, such as,for example, a fabrication environment using photolithography systems.The low molecular weight species, such as acetone, isopropyl alcohol andlow molecular weight siloxanes are the most prevalent in manufacturingenvironments. Compounds that are most likely to reduce the performanceof optics are compounds having a high contamination coefficient or ahigh molecular weight examples can include, but are not limited to,methoxytrimethyl silane, trimethyl silane and trimethyl silanol. Thesecompounds appear in italics in Table 1 have a higher molecular weight,higher contamination coefficient and an inorganic component. Compoundsthat negatively impact optical systems may also be described and includerefractory compounds such as silanes, siloxanes and iodates, inparticular hexamethyldisiloxane (C₆-siloxane). TABLE 1 Typicalconcentration, Compound (in clean rooms) ppbV Isopropyl Alcohol 610.0Acetone 330.0 Ethanol 134.0 Silane,Methoxytrimethy/- 35.0Heptane,Hexadecafluoro- 28.0 2-Pentanone 17.0 2-Butanone (MEK) 9.8Hexane,Tetradecafluoro- 8.9 Butanoic Acid,Heptafluoro- 5.2Tetrahydrofuran 3.3 3-Buten-2-one 2.5 4-Methyl-2-pentanone (MIBK) 1.9Silane,Trimethy/(1-Methy/ethoxy)- 1.7 n-Pentane 1.4 Silanol,Trimethy/-1.4

Optics design also affects the relative sensitivity of the system tocontamination. For example, light transmission is important intransmissive optical systems, like windshields, wherein reflectanceapproaches zero. High reflectivity systems, where transmissionapproaches zero, are inherently twice as contamination sensitive astransmissive optical systems because photons pass through anycontaminating film twice, whereas light energy is only absorbed orscattered once in transmissive systems.

Describing the effect of molecular films on optical surface propertiesin terms of mathematics yields equation 1, for reflectance, and equation2 for transmission.ρx(λ)=ρ(λ)exp[−2αc(λ)x]  Equation 1τx(λ)=τ(λ)exp[−αc(λ)x]  Equation 2Where:

-   P=reflectance-   α=absorbance-   τ=transmittance-   λ=wavelength-   αc=absorbance of a contaminating film, empirically determined

Both transmitted and reflected energy, which is information used inlithography instruments and tools in semiconductor fabrication systems,drop exponentially with the accumulation of molecular films on opticalsurfaces. In lithography processes, the first order effect of molecularfilms on lenses is typically a reduction in light intensity due toenergy absorbance by the contaminating film. These transmission lossesreduce the number of wafers processed per hour, and consequently reduceproductivity. This is analogous to the power reductions in spacecraftsolar arrays, caused by accumulating molecular films. Secondary effects,in lithography processes, involve a reduction in image uniformity, whichreduces critical dimension uniformity and yield.

Photochemical decomposition reactions occur when high-energy photonsinteract with organic vapors. These reactions form extremely reactivefree radicals from otherwise neutral and relatively inert organicmolecules. Irrespective of where radical formation occurs, in the gasphase or on the surface of optical elements, the resulting free radicalsmay react to form much larger organic compounds, which can contaminateoptical elements. In severe cases, a polymer layer may be formed on theoptical surface. The relationship between the chemical nature of theorganic species and wavelength of light it absorbs can affect the natureand severity of optics contamination. For example, I-line or 365 nmwavelength light is energetic enough to break down only a few iodatedcomponents, which are not commonly found in clean room air. 248 nmwavelength light, typically used in deep ultraviolet (DUV) lithographyfor fabricating 250 to 150 nm linewidth devices, is more efficient andreacts with most halogenated organics and may even interact with somecommon hydrocarbons. 193 nm light, required for less than 130 nmgeometries, reacts very efficiently with a wide range of airborne orgaseous molecular organic contaminants. 157 nm optical elements are evenmore sensitive to environmental conditions than 193 nm optics becausethis wavelength of light is efficiently absorbed or interacts withnearly all organic species plus oxygen and atmospheric moisture,requiring the exposure area, the area between the final optical elementand the wafer, commonly called the free working area, to be purged withan inert, clean, dry, oxygen-free gas.

As the wavelength of light used in the lithography exposure tooldecreases, the energy per unit photon increases. These progressivelyhigher energy photons stand a better chance of breaking the bonds of anumber of commonly present molecular species, ultimately rendering theminto reactive species that stick to optical surfaces. The overallstructure of a molecule plays a significant role in the ability of aphoton to break any specific bond. Table 2 summarizes opticscontamination as the lower wavelengths of electromagnetic spectrum areused to provide for the fabrication of smaller features.

Atmospheric pressure, low K1 factor optical lithography for less than150 nm critical dimension on 300 mm wafer substrate device productionmay be the basis of advanced Integrated Circuit (IC) production in thenear term. In these technology nodes, lithography-induced criticaldimension variations have a particularly acute affect on devicecharacteristics. For example, the standard deviation of propagationdelay times for CMOS based ring-oscillators increases from 1% for 300 nmdevices to 20% in 250 nm devices. Variations in gate oxide, impurity,and gate lengths were the primary causes of variations in device delaytimes. Below 200 nm gate length, however, the impact of gate lengthvariation accounts for a remarkable 80% of the effect. The criticalityof dimension variation in 150 nm lithography, for example, has lead to acritical dimension control budget of 15 mn, post-etch, 3 sigma. Sinceexposure dose and image resolution are compromised by opticscontamination in proportion to the location and thickness of thecontaminating film, contamination needs to be prevented before itoccurs. TABLE 2 Issue λ = 248 nm λ = 193 nm λ = 157 nm CommentsPropensity to Low Moderate Nearly Assumes form vapor photo-concentration deposits the low ppb nitrogen range (<10 ppb O2) Abilityto Low Moderate High Based on photoclean absorption surfaces in-coefficients using active organic layer oxygen absorbance InteractionsAromatics Aromatics Nearly all Interaction hydro- moderate very hydro-determines carbons absorbance other weakly carbons allowable absorb ofbefore lens performance suffers

Existing methods of contamination control in lithography involves theuse of activated carbon filters and/or some combination of adsorptiveand chemisorptive media to adsorb or chemisorb the contaminants in airand gas streams that come in contact with the lens surfaces. In somecases, periodic regeneration of the adsorptive beds by thermaldesorption occurs.

Passive adsorption is unable to practically capture and retain thelighter hydrocarbons, oxygen, and water that interfere with imagingusing 193 nm and 157 nm light. The propensity to form photodeposits,ability to photoclean, and interaction of hydrocarbons is tabulatedrelative to different wavelengths of light in Table 2.

Filter systems for contamination control are described in U.S.application Ser. No.: 10/205,703, filed on Jul. 26, 2002 entitled“Filters Employing Porous Strongly Acidic Polymers and PhysicalAdsorption Media”, now U.S. Pat. No. 6,761,753, U.S. application Ser.No.: 09/969,116, filed on Oct. 1, 2001 entitled “Protection ofSemiconductor Fabrication and Similar Sensitive Processes”, and U.S.application Ser. No. 09/783,232, filed on Feb. 14, 2001 entitled“Detection of Base Contaminants In Gas Samples”, now U.S. Pat. No.6,855,557, the entire teachings of the above referenced patents andapplications being incorporated herein by reference in their entirety.

FIG. 1 is a graphical representation 20 of contamination coefficient 22versus a molecular weight 24. Note that a higher contaminationcoefficient means that it is more likely to contaminate system optics.The nearer term 193 nm wavelengths show some correlation between thecontaminants molecular weight and its ability to contaminate the lens.Consequently, while the higher molecular weight species are of greaterimmediate concern for lens contamination, the lower boiling pointmaterials, which are typically in higher concentration in semiconductorcleanrooms as shown in Table 1, can become a concern due to their muchhigher concentration and ability to adsorb photon energy atprogressively shorter wavelengths. Moreover, particularly at 157 nm,oxygen and water need to be removed from the light path because theyalso absorb photon energy.

Existing systems have many disadvantages including passive adsorptionsystems that do not effectively remove low molecular weight organicmaterials; the removal efficiency and capacity of passive adsorptionsystems are proportional to the concentration of the impurities. In thisapplication, the inlet concentrations are very low, making efficiencyand capacity correspondingly low; and on-site regeneration of passiveadsorption beds requires periodic temperature increases to regeneratethe beds. Since most advanced lithography systems must maintain air andgas temperature stability at typically less than 100 milliKelvin, toavoid heating or cooling the optics, which change their opticalcharacteristics, this strategy is impractical in advanced lithography.

FIG. 2 is a graphical representation 30 illustrating a comparison of apreferred embodiment of the system for determining contamination withrespect to sample mass in a collection device or contamination trap andsampling time in accordance with the present invention and the priorart. An extended duration sample time, sample time 40, is used whereinthe gas sample volume is not limited by the low molecular weightbreakthrough volume, as is the case with the prior art method usingsample time 38. In a preferred embodiment, the sampling time is at leastsix hours long and is preferably in a range of six hours to twenty-fourhours. Higher capacity traps yielding longer collection times may benecessary for certain applications.

The extended time sampling method in accordance with a preferredembodiment of the present invention, collects higher masses of highermolecular weight compounds, which contribute to the contamination in thegas supply and which reduce the performance of optical elements more sothan lower molecular weight compounds. Both high and low molecularweight compounds contribute to the contamination level but are operativeat different rates. The high molecular weight compounds contribute tofirst order contaminating effects as they cause more damage to theoptical systems even if present at low concentrations than low molecularweight compounds which contribute to third and fourth order effects. Thecollection device in accordance with a preferred embodiment is drivenbeyond saturation or breakthrough capacity to quantitatively measure theequilibrium concentration of low molecular weight compounds. Thebreakthrough volume is the amount of gas sample volume required to gobeyond the absorbent capacity of the collection device. It should benoted that contaminates may be inorganic materials which may be carriedby organics to the optical element. This extended time sampling methodcan also use different types of sample collecting media including thosewith adsorptive properties close to that of the optical surfaces ofinterest.

A preferred embodiment of the present invention includes “glass” or“coated glass” based adsorptive contamination traps. These contaminationtraps have not been used in the past due to their limited ability tocollect and retain lower molecular weight species. These materials havesurface properties identical or similar to properties of the opticalelements used in the optical systems of photolithography tools. Othermaterials that emulate the surface properties of these optical elementsthat generate contamination can also be used.

In a preferred embodiment, the extended time sampling method may beextended from a few hours to several days and even weeks. The amounts ofanalyte collected represents the average value over time for compoundsthat have not reached their breakthrough time as illustrated by line 36at sample time 2, line 40, and an average equilibrium concentration forthose species that have already reached their breakthrough volume asillustrated by line 34 at sample time 2, line 40.

With respect to higher molecular weight species, the internal surface ofthe sampling lines and/or manifolds are kept at equilibrium with the gasphase sample, and therefore do not interfere with the sample collectionprocess. In a preferred embodiment, between sampling sessions, flowthrough the sampling lines and/or manifolds is maintained.

FIG. 3 is a graphical representation 50 illustrating spectral analysiscomparisons of the system and method of determining contamination inaccordance with a preferred embodiment of the present invention and theprior art. The extended time sampling method of the present inventionoffers better sensitivity for components having high boiling points asillustrated by lines 52, 56. The results of the extended time samplingmethod in accordance with a preferred embodiment of the presentinvention better represent contamination on the optical surface, giventhe improved high molecular weight sample collection method of thepresent invention. A preferred embodiment of the system of the presentinvention provides the ability to use the actual optical surface ofinterest as the collection medium which in turn allows alignment ofsampling surface properties and optical surface properties therebymaking the analysis results more meaningful to the prediction of opticscontamination.

The extended time sampling method in accordance with a preferredembodiment may reduce and preferably eliminate the uncertainties ofsample loss on sample lines and/or manifolds. The extended time samplingmethod's simplicity minimizes the effect of uncontrolled contaminationby personnel deploying the traps. Consequently, less training andexperience are required to collect samples.

FIG. 4 illustrates graphically surface coverage as a function ofcontamination level showing greater surface mass coverage per unitconcentration in accordance with a preferred embodiment of the presentinvention. FIG. 4 illustrates this relationship for higher molecularweight components at the upper left with the lower molecular componentstowards the lower right of the graph. For a given concentration, thehigher molecular weight compounds collect on surfaces more readily thando lower molecular weight species. One of the problems with the priorart method is that due to the shorter sampling times, much of whatlittle sample is available for collection collects on the sample tubewalls and manifold surfaces, all upstream of the collection trap, andnever reaches the trap. This phenomenon causes a further loss of highmolecular weight sample mass. Moreover, heated sampling lines and/ormanifolds, which could ameliorate the problem, are not practical in theproduction cleanroom environment.

FIG. 5 is a diagram of a preferred embodiment of a system 100 fordetermining contamination in accordance with the present invention. Thepreferred embodiment of the apparatus includes a tubular collectiondevice 102 having an inlet port 104 and an outlet port 106. In apreferred embodiment, the collection device includes, absorptivematerials 108 such as, for example, glass spheres of a given size. In apreferred embodiment, crushed glass spheres are used. In anotherpreferred embodiment, the absorptive material 108 is the polymer Tenax®supplied by, for example, Supelco. Tenax® has a high capacity for highboiling point compounds and operating Tenax® past low molecular weightbreakthrough capacity allows the capture of a meaningful and analyzablemass of high molecular weight compounds. To collect a sample, an end capin the inlet post is removed, allowing gas from a gas source to passthrough the inlet port 104. Laser light may be directed through thesampling tube in a preferred embodiment of the present invention. Thefree radicals of the contaminants present in the gas sample may bondwith the absorptive media 108 in the collection device 102.

In a preferred embodiment of the system for controlling contamination,multiple sample tubes and blank collection devices may be used. Thecollection device or refractory trap is applicable to both high pressuresampling, for example, purge gas, venting to the atmosphere assumingsufficient pressure and filter sampling, wherein the traps are connectedto a vacuum source. The flow is controlled by an easily changeablecritical orifice.

In a preferred embodiment, the trap contains three sample tubes, oneblank and two active sample devices. Chemical analysis of the data maybe correlated to transmission or image uniformity loss of thelithography tool, for example, using a regression analysis which weightsfirst, second, third and fourth order effects: Uniformity or Intensity=a[C₆-siloxane]+b[C₆-C₃₀]+c[C₃-C₆]+d[C₁-C₅] herein the parentheticexpressions are indicative of the concentration of species. First andsecond order contaminating effects have a greater impact oncontamination of optical systems than third or fourth order contaminantsand typically show a greater contamination coefficient (e.g. a>b>c>d).The first order contaminants may comprise high molecular weightrefractory organics such as, for example, C₆ siloxanes and C₆ iodidewith an inorganic component which is not volatilized through combinationwith oxygen. Second order contaminants may comprise high molecularweight organics, such as, for example, compounds including carbon atomswithin the range of approximately six to thirty carbon atoms (C₆-C₃₀).Third order effects can arise due to the contaminating effects oforganics such as C₃-C₆ that have approximately three to six carbonatoms. Further, fourth order contaminants Include organics such as, forexample, methane, that have approximately one to five carbon atoms.

In preferred embodiments of the system in accordance with the presentinvention, a refractory trap may be used both upstream and downstream ofany in-line filtration system. FIG. 6 is a preferred embodiment of arefractory trap system 120 in accordance with the present invention. Asdescribed herein before refractory compounds include at least siloxanessuch as, for example, hexamethyldisiloxane (C₆), silanes such as, forexample, C₃-silane, silanes such as, for example, C₃ and iodates. Therefractory trap system 120 includes a conduit 121 in communication witha gas source and through which a gas sample is carried with pressuresranging between approximately 1 to 120 psi. The gas sample is carrieddownstream to a pressure cavity 122. A pressure relief valve 123 allowsthe continuous flow of gas to ensure that the pressure cavity walls arein equilibrium with the gas phase of the gas sample. The refractory trapsystem 120 includes active sampling traps or collection devices 124 anda blank trap 125 in the trap cavity 126. The active sampling trapelements 124 may include an absorptive medium such as, for example, thepolymer Tenax®. The gas sample flow in active elements is approximately0.11 lpm. The blank trap 125 is not in communication with the gas sourceor pressure cavity and as such is not removing any contaminants. Theoutflow gas stream from the active collection devices 124 flowsdownstream into a manifold 127 which is in fluid communication with avacuum line 130, via an orifice 129. A pressure/vacuum regulator valve108 is disposed between the manifold and the orifice 129 to regulatepressure. The refractory trap system 120 provides for both a lowpressure application or a high pressure application using a singledesign.

In a preferred embodiment, the gas supply may include a particularconstituent such as hydrogen gas which may be used to clean the surfacesof the collection devices or, surfaces of optical systems that have beencontaminated by a surface contaminant, for example, SiX. The gasadditive combines with the surface contaminant to form a volatilecompound that is then purged from the system. For example, SiX combineswith hydrogen gas to form silane (SiH₄) which is volatile and is purged.The purge gas, is preferably in the ultra high purity gas level allowingthe collection device to be placed upstream and downstream of typicalin-line filters.

A sample report derived from a collection device may comprise thefollowing information:

-   Contact information: Name, address, phone, email of person sending    the sample-   Tool #:-   Gas sampled: N2 Air-   Sample location:    -   Upstream of filter    -   Downstream of filter    -   Interstack-   Sample start date:-   Sample end date:-   Date received:-   Report date:-   Upstream Sample:-   C2-C5: X ppb*(*equilibrium concentration)-   C₆-C₃₀: Y ppb-   Total siloxanes: z ppb-   Total sulfur compounds:-   Past history on this sample location:

In another preferred embodiment the collection device is locateddirectly in contact with the airstream, thereby avoiding sample linecontamination and using either passive diffusion or an active flow tocollect the sample.

FIG. 7 is a flow chart of the method 150 of detecting and removingcontamination in accordance with a preferred embodiment of the presentinvention. The method includes the step 152 of delivering a gas sampleto a collection device. In a preferred embodiment, the collection deviceis as described with respect to FIG. 5 and/or FIG. 6. The method furtherincludes the step 154 of absorbing contaminants contained in the gassample in the collection device. The collection device is configured toemulate the environment of surfaces of optical elements. The method 150includes the step 156 of maintaining the gas sample in the collectiondevice for an extended duration sampling time which represents operationof the collection device past the saturation or breakthrough capacity ofthe device, for at least the lower molecular weight species. Asdescribed herein before the extended duration sampling time enables thecollection of an equilibrium concentration of low and preferably highmolecular weight compounds.

The internal surfaces of the sampling lines and manifolds are inequilibrium with the gas phase sample in order to not interfere with thesample collection process. In a preferred embodiment, the method 150includes maintaining the flow of the gas sample through the samplinglines and manifolds.

In accordance with another preferred embodiment, the system of thepresent invention comprises a photolithography cluster tool, forexample, an exposure tool, used in manufacturing semiconductor devices,that is sensitive to molecular contamination and a filtering systemwhich removes the molecular contamination which may include volatile andsemi-volatile or condensable organic substances, causing contaminationof optical elements via series of homogeneous and/or heterogeneousultraviolet (UV) induced processes. These optical elements are containedtypically within a light path of a photolithography tool. In accordancewith a preferred embodiment of the present invention, the filteringsystem for the ultra-purification of compressed fluids, for example,nitrogen, air or other suitable gases for purging of optical elements,with organic constituents comprises a membrane module, which separatesthe components of a given gas mixture by means of their differenttransport rates through the membrane. High removal efficiency of organiccontaminants, in particular of first and second order contaminants maybe obtained due to selective permeation on glassy polymers such as, forexample, polyetherimide or rubbery polymers such as, for example,silicone rubber and also on porous ceramic membranes which generallyhave extended temperature limits up to approximately 300° C. Water andoxygen are preferably also removed using the membrane as they candegrade light transmission along the optical path in the system.

Membranes are generally available in two morphologies: homogeneous orcomposite. In the latter, thin polymeric permselective “skin” isdeposited on a preformed porous substrate, which need not be the samepolymer and may or may not interact with permeate. Polymeric membranesmay be cast into various shapes: flat sheets for plate and frame andspiral wound modules, in the latter sheets and separating screens arewound into sandwich like structure by rolling around central permeatetube and self-supporting fibers, for example, hollow fibers andcapillary membranes.

In a preferred embodiment as illustrated in FIG. 8 the filtering system170 comprises a filtration module based on a selectively permeablemembrane 186 to filter organic compounds from a gas stream such as, forexample, a nitrogen stream. The selectively permeable membrane may be ofthe type such as supplied by, for example, Membrane Technology &Research, Inc. In this preferred embodiment, the feed flow 174 isnitrogen that contains some amount of organic contamination. The feedflow may comprise 99-100% nitrogen with any balance in organiccontaminants as well as water and oxygen. Assuming 90% removalefficiency of the membrane, the composition of the residue is purifiedby a factor of 10. The composition of the permeate stream can beenriched with organic contaminants. The filtering system 170, inaccordance with a preferred embodiment of the present inventionpreferably removes contamination effects of first through fourth ordercontributors.

In another preferred embodiment the filtering system 170 comprises afiltration module based on a selective membrane 186 to filter organiccompounds from a gas stream 174 wherein the collection device or pipe172 is connected to a vacuum source to increase the pressure gradientacross the membrane 186 to increase membrane efficiency. In thisembodiment the feed flow 174 is nitrogen that contains some amount oforganic contamination. In a particular embodiment the feed flow, 174 caninclude nitrogen with organic contaminants as indicated above. Assuminga 99% removal efficiency of the membrane, the composition of the residue176 is again improved by a factor of 10 for nitrogen and the balance inorganic contaminants. The composition of the permeate stream 178 isfurther enriched with organic contaminants.

In another preferred embodiment, the filtering system 170 comprises afiltration module based on a selective membrane 186 to filter organiccompounds from a gas stream. In this particular embodiment the feed flowis nitrogen that contains some amount of organic contamination. The feedflow 174 comprises 99-100% nitrogen with the balance being organiccontaminants. Assuming 90% removal efficiency of the membrane, thecomposition of the residue 176 is 99-100% nitrogen and the balance inorganic contaminants. The composition of the permeate stream 178 may beenriched with organic contaminants. The organic contaminant enrichedairstream 178 is then directed to a regenerative adsorption device forpurification. The permeate stream 178, which has been purified by anadsorption bed system, is then returned to the feed flow. This filteringsystem in accordance with a preferred embodiment of the presentinvention reduces the loss of feed flow volume.

In another preferred embodiment, the filtration module consists of acomposite membrane, a support of which is pretreated with a solidelectrolyte washcoat and an oxide catalyst to promote electrochemicaldecomposition of the permeate 178 within the support at relatively lowtemperature.

In another preferred embodiment, the filtering system 170 comprises afiltration module based on a selective membrane 182 to filter organiccompounds from a gas stream. In this embodiment, the feed flow 174 isnitrogen that contains some amount of organic contamination. The feedflow comprises 99-100% nitrogen with the balance being organiccontaminants, oxygen, and water. Assuming 90% removal efficiency of themembrane, the composition of the residue is again improved by a factorof 10 for nitrogen with the balance being organic contaminants, but themembrane may not be selective enough to remove oxygen and water.Accordingly, the residue 176 of the filter system 170 is then directedto a second filter system, of similar mechanical construction to thefirst, which contains a different membrane specifically selected toallow oxygen and water to traverse the membrane, but is, again, lesspermeable to nitrogen. The residue of this second filter system may nowbe substantially free of organics, water, and oxygen which are allhazards to advanced lithography processes. Again, the composition of thepermeate stream may be enriched with organic contaminants, water, andoxygen.

This filtering system can be used to purify nitrogen, synthetic air,clean dry air, all gas streams used in advanced photolithography, or anyother compressed gas used in semiconductor processing. It may be,however, advantageous to filter synthetic air prior to mixing, forexample, filter oxygen and nitrogen separately, before mixing themtogether to make synthetic air.

The filtering system may be constructed without limitation in a numberof ways such as, for example, rolled-up supported membrane, rolled upself-supporting membrane, membrane disposed on a prefabricated poroussupporting structure, a cylindrical pleated air filter, or comprisehollow fiber bundles through which the feed flow is directed.

The preferred embodiments of the filter system of the present inventionremove both high and low molecular weight organic compounds and otherunwanted contaminants such as water vapor, oxygen, inorganic impurities,effectively, and with a low concentration feed flow. In addition, thefilter systems of the present invention operate continuously withoutfilter replacement or pressure, flow, or temperature change ordisruption. The preferred embodiments of the present invention addressthe problems of the prior art filters which have a limited capacity forlow molecular weight hydrocarbons and rely on regenerative thermalcycles, which cause instability of the output gas temperature. Thepreferred embodiments of the filtering systems of the present inventionprovide an unlimited capacity for removing low molecular weighthydrocarbons and other contaminating species, independent of feed flowconcentration, produce no sudden changes in the output flow conditions,and are easy and inexpensive to maintain.

FIG. 9A illustrates a schematic block diagram of a filter device havinga bed showing the retention of different species in the bed inaccordance with a preferred embodiment of the present invention. Thispreferred embodiment takes advantage of the inherent property ofphysioadsorbants to show different retention times for differentspecies. For example, lower molecular weight species move through thecarbon bed 252 more rapidly than do higher molecular weight species. Asdescribed hereinbefore, certain higher molecular weight species may bemore contaminating to a process than lower molecular weight species.Accordingly, measurements are taken at a location upstream, in themiddle of the chemical filter bed 252 or in an alternate preferredembodiment between two in-series filters, and at the discharge ofrelatively fast moving (moving through the filter bed) species,hereinafter referred to as leading indicator gases as indicators of theimminent breakthrough of the more slow moving species.

FIG. 9B graphically illustrates the efficiency of the filter bed withrespect to time by measuring the different species in accordance with apreferred embodiment. In a preferred embodiment, the target gas is an C₆organic contaminant which may, or may not, contain an inorganic atom,and the leading tracer gas is a C₅ organic species. The detector systemin a preferred embodiment includes a thermal desorption preconcentratorcoupled to a gas chromatograph with flame ionization detection. Thissystem achieves the sensitivity the system requires to perform reliablelow concentration work. Samples of the leading tracer gas are taken atvarious locations in the filter, before or after the filter or betweentwo filters, for example, filter 1 and 2. The performance of the filtercan be illustrated on a graphical user interface included in the system.

FIG. 10 is a flowchart 290 of a method for monitoring the performance ofa gas phase filter system in accordance with a preferred embodiment ofthe present invention. The method includes the generation of a numericalrepresentation of the chromatogram of the gas flow upstream of thefilter per step 292. Per step 294 the target polluting species areselected as the target is present at a detectable level upstream. Instep 296 the non-polluting species that are the leading indicators areselected that are closest in elution (removing of absorbed material fromadsorbent) time and greater than and equal to the concentration oftarget species of interest. The leading indicator tracer gas travelsfaster than the target pollutant through the filter bed. The methodincludes measuring the non-polluting species in different locations, forexample, at a location prior to the filter bed, at a location in themiddle of the filter bed and at a location at the discharge of thefilter bed. The breakthrough of the target pollutant is then assessedand determined by the measurement of the leading indicator (tracer gas)as detected by a detector system per step 300.

A method for monitoring the performance of a gas-phase filter positionedin an air stream, which may be subject to molecular contamination, anduseful for removing molecular contamination therefrom includes samplingthe airstream at a location upstream of the air filter so that a varietyof upstream molecular contaminants are detected and a target pollutantand a tracer gas are identified. The tracer gas travels faster than thetarget pollutant of interest in the filter. Further, the method includessampling the airstream at a location downstream of the air filter sothat the tracer gas is detected over time. The method includesdetermining the performance of the filter with respect to the targetpollutant using a method that establishes a correlation between the lowmolecular weight compounds and the high molecular weight compounds andthus determining the performance of the air. In a preferred embodiment,the method includes sampling the airstream at a location in the middleof the filter bed.

FIG. 11 is a schematic diagram of a system 320 that includes a filtersystem in accordance with a preferred embodiment of the presentinvention. The gas flow or airstream 322 input into the filter 324 issampled by a detector system. The filter bed includes a physioadsorbentto chemically adsorb contaminants. The air flow in the middle of thefilter bed is also sampled and analyzed using a sampling port 326 thatprovides the sample to the detection system. The location of thesampling port 326 with respect to the outlet is proportional to thepropagation rate of the leading indicator gas, for example, if thepropagation rate of the tracer gas is high then the distance of thesampling port 326 from the outlet is raised. The discharge flow 328 atthe outlet of the filter 324 is also sampled. A position selectablevalve 336 disposed in the inlet of the detection system providessampling capability for more than one stream. Thus, the sampled flowfrom the inlet of the filter bed, the middle of the filter bed or theoutlet of the filter bed can be selected as input into the detectionsystem. A valve 338 allows for the selection of the flow into apreconcentrator 340 or into a bypass 342. A pump 346 for thepreconcentrator provides adequate flow therein. The discharge of thebypass or the preconcentrator is then selected by the valve to then forman input into a chromatographic column 350. A heater 348 is disposedaround the chromatographic column 350. The outlet of the column formsthe input of the detector 352 having a flame ionization detectionsystem. The spectrum illustrating the abundance of the constituentsdetected with respect to time is displayed on a graphical user interface358.

The preferred embodiment uses detection technology which is inherentlysensitive to, and can identify and quantify organic species at very lowconcentrations, for example, below 1 ppb (V) using, for example, gaschromatograph/flame ionization detection (GCFID). The preferredembodiments of the present invention provide advanced warning of filterfailure without actually jeopardizing the process by allowing the actualspecies of interest to breakthrough. The preferred embodiment does so ata low enough concentration to be meaningful to highly sensitiveprocesses, like optics systems.

In a preferred embodiment the filter includes a bed of the polymerpellets exposed to the airstream using a traditional media tray and racksystem. In an alternative preferred embodiment the filter includes ahoneycomb configuration with the polymer pellets held in a partiallyfilled or completely filled honeycomb structure. Other embodimentsinclude filter construction including, but not limited to, a monolithicporous or honeycomb structure formed from polymer, a mat of polymerfiber, either woven or nonwoven, pleated and arranged in a traditionalair filter, a bed of the activated carbon pellets exposed to theairstream using a traditional media tray and rack system, a honeycombconfiguration wherein the activated carbon pellets are held in apartially filled or completely filled honeycomb structure, a monolithicporous or honeycomb structure formed from the activated carbon, a mat ofactivated carbon fiber, either woven or nonwoven, pleated and arrangedin a traditional air filter and a carbon based composite filterconstructed of woven or nonwovens support structures.

In preferred embodiment the detection system may include any system thatis capable of measuring organic compounds at very low concentrationsincluding, but not limited to a GCFID with, or without apreconcentrator, a GCMS with, or without a preconcentrator, aphotoacoustic detector with, or without a preconcentrator, and IMNSwith, or without a preconcentrator, or any combination thereof.

In a preferred embodiment reactive inorganic materials, includingmolecular bases and molecular acids are included in the airstream. Thesecompounds may react to form nonvolatile salt particles. Molecularcondensable high boiling point organic materials which may be adsorbedon the optical elements and undergo DUV light induced radicalcondensation or polymerization. Resulting polymer films in some casesmay be removed by active oxygen treatment species. Refractory materialsare compounds containing atoms forming nonvolatile or reactive oxides,for example, but not limited to, P, Si, S, B, Sn, Al. These contaminantsmay be exposed to DUV light and may form refractory compounds resistantto active oxygen treatment.

In a preferred embodiment molecular bases and molecular acid samples arecollected using impingers filled with distilled water (10 cc). An air(gas) sample is drawn through the impinger at 1 L/min for 240 minutesusing a programmable sample pump. The total sample volume in a preferredembodiment, without limitation is 240 L.

Further, in a preferred embodiment, molecular condensable high boilingpoint organic materials and refractory material samples are collectedusing Thermodesorbtion Samplers (TDS) filled with porous medium, forexample, Tenax® T.A. An air (gas) sample is drawn through the collectionmedia at a flow of the 0.15 L/min for 240 minutes, using a programmablesampling pump with low flow adapter. Total sample volume isapproximately 36 L. In preferred embodiments, the flow rate can vary ina range 50 cc/min to 250 cc/min. The temperature can also vary fromapproximately room temperature to approximately −100° C. Field blank orempty samples are collected for each type of sample. The field blank isa sample device (impinger of TDS), which is handled in the field thesame way as an actual sample having zero sample volume drawn through.The purpose of the field blank is to detect possible uncontrolledcontamination events during sample handling and transportation. Fieldblanks are analyzed in the same manner as actual samples.

In a preferred embodiment, analyses of molecular bases and molecularacids samples includes using Ion Chromatography methods. Compounds areidentified by retention time and quantified using individual calibrationstandards and a 10-point calibration procedure. Low Detection Limit(LDL) of the corresponding methods is 0.1 ug/m³ per individualcomponent. In a preferred embodiment, molecular bases and refractorymaterial samples are analyzed using a Gas Chromatograph (GC) equippedwith a Mass selective Detector and Thermal Desorption System (TD). Thetotal analytical system (TD/GC/MS) is optimized to separate and quantifyanalytes with a boiling temperature of hexane and higher with LDL of−0.1 ug/m³ per individual component. Individual components areidentified by a MS library search and chromatographic peak position.Individual component are quantified against two analytical standards,for example, toluene and hexadecane. Analytical results are listed inthe Tables 3-9. TABLE 3 N2- N2- Concentration, ug/m3 facilitiesfacilities Oil free Air Oil free Air before after before after Fabambient Sub Fab Ammonia (as NH3) 0.4 <0.1 0.4 <0.1 4.2 6.4 Otherinorganic <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 acids Nitrous acid (as <0.1 <0.10.8 <0.1 0.8 1 NO2) Nitric acid (as NO2) <0.1 <0.1 <0.1 <0.1 <0.1 <0.1C₆ + Organic −1.1 −0.9 −.0.8 −.2.3 −213 H Compounds (as toluene)

TABLE 4 Concentration, ug/m3 Compound as toluene as hexadecane Benzene(78) 0.4 0.2 Silane,Dimethoxydimethyl (59) 2.7 1.2 Hexane,3-Methvl (26)0.4 0.2 2-Heptane (47) 0.5 0.2 Silane,Trimethoxymethyl (45) 0.4 0.2Hexane,2,5-Dimethyl (33) 0.3 0.1 Toluene (82) 1 2.9 1.3 Propanoicacid,2-hydroxy-ethyl ester (59) 2 1.5 0.7 PGMEA (92) 3 2.2 1Ethylbenzene (59) 4 3.2 1.3 n-Propylbenzene (56) 0.3 0.1 Cyclohexane(84) 9.5 0.2 Xylenes (48) 5 15.2 6.1 Styrene (59) 0.3 0.11,2,3Trimethylbenzene (72) 1.8 0.7 1,3,5Trimethylbenzene (60) 0.6 0.2Cyclohexanone (77) 6 0.6 0.2 3-Heptanone (47) 0.4 0.2 Unknown 0.5 0.2Unknown 0.7 0.3 Octane,2,6-Dimethyl (59) 7 0.3 0.1Cyclohexane,(1-Methylethyl) (40) 0.4 0.2 Nonane (59) 0.4 4.1Octane,2,5,6-Trimethyl (53) 4.3 1.7 Octane,2,2,7,7-Tetramethyl (53) 1.80.7 Octane,2,2,6-Trimethyl (64) 1.4 0.6 Benzene,1-Ethyl,3-Methyl (93) 83.1 1.2 Decane,2-Methyl (77) 1.2 0.5 Benzene,1-Ethyl,2-Methyl (77) 0.90.4 Benzaldehyde (48) 9 2.8 1.1 Carbamic acid,methyl-phenyl ester (25)2.1 0.8 Propylene cabonate (86) 10 3.5 1.4 Heptane,2,2,4,6,6-Pentamethyl(64) 2.6 1 Decane,2,2″Dimethyl 64) 11 5.7 4 Decane2,2,9-Trimethyl (77)12 10.1 2.3 Nonane,3,7-Dimethyl (67) 13 17 0.2 Decane,5,6-Dimethyl (50)1.7 0.7 Decane,2,3-Dimethyl (40) 1.9 0.8 Nonane,3-Methyl-5-propyl (64) 31.6 Decane,2,6,7-Trimethyl (47) 14 1 6Heptane,4-Ethyl-2,2,6,6-Tetramethyl (72) 15 14 0.2 Undecane,2,5-Dimethyl(59) 1 0.2 Undecane,4,6-Dimethyl (59) 16 1 4.8 Undecane,3,5-Dimethyl(53) 1 0.7 Undecane,4-methyl (83) 2 1 Nonane,3-methyl-5-propyl (64) 17 52.3 Undecane,5,7-Dimethyl (43) 1 0.7 Undecane,3,8-Dimethyl (38) 2 1Dodecane,2,5-Dimethyl (36) 3 1.4 Heptane,2,2,3,4,6,6-Hexamethyl (72) 10.6 Dodecane,2,6,10-Trimethyl (72) 2. 0.9 Tridecane,5-Methyl (64) 0. 0.3Tridecane,4-Methyl (64) 0. 0.2 Dodecane (50) 0. 0.2 Benzoic acid (66) 189. 4 Cyclotetrasiloxane,Hexamethyl (39) 0. 0.2Cyclotetrasiloxane,Octamethyl (54) 0. 0.22,5Cyclohexadiene-1,4-dione,2,5,-diphenyl (97) 2 10.1 Total 21 73

FIGS. 12A-12C are graphical illustrations of chromatograms of a gassample including an average ion scan of the spectra end (FIG. 12C) inaccordance with a preferred embodiment of the present invention. The gassample is fabricated ambient air.

The mass spectrometry (MS) results for sub-fabricated air are listed inTable 5. TABLE 5 Concentration, ug/m3 Compound as toluene as hexadecaneHexane (78) 0.4 0.2 Benzene (84) 0.5 0.2 3-Pentanone,2,4-Dimethvl (72)0.2 0.1 Hexanal (64) 0.3 0.1 Propanoc acid,2-hydroxy,propyl ester (56)0.4 0.2 Propanoc acid,2-oxo-ethyl ester (29) 0.1 0.05 Toluene (79) 1 3.31.4 3-Pentanone,2,4-Dimethyl (36) 0.2 0.1 2,3-Dimethyl Pentane (21) 0.40.2 Propanoic acid,2-hydroxy,propyl ester (57) 0.4 0.2 Propanoicacid,2-oxo-ethyl ester (27) 0.1 0.05 PGMEA (59) 0.8 0.3 Ethyl Benzene(61) 4 7 4.9 Styrene (39) 0.3 0.1 Xylenes (35) 5 35 17.51,2,4-Trimethylbenzene (67) 1.4 0.6 Nonane (61) 0.7 0.32-Furanol,tetrahydro-2-Methyl (56) 1.1 0.5 Cyclohexanone (73) 6 92 40Octane,2,5,6-Trimethyl (50) 7 1.7 0.7 Benzene,1-Ethyl-3-methyl (91) 82.2 0.9 Decane,3,4-Dimethyl (59) 0.4 0.2 Benzene,1-Ethyl-2-methyl (72)0.5 0.2 Alpha-methylstyrene (96) 1.1 0.4 Heptane-2,2,4,6,6-Pentamethyl(42) 0.8 0.3 Benzaldehyde (96) 9 0.9 0.4 Decane,2,2-Dimethyl (64) 11 1.70.7 Decane,2,2,9-Trimethyl (53) 12 4.2 1.7 Nonane,3,7-Dimethyl (47) 134.7 1.9 Benzene,1,3,5-Trimethyl (91) 0.6 0.2 Undecane,3,6-Dimethyl (38)1 0.4 Decane,2,6,7-Trimethyl(53) 14 4.2 1.7 1-Hexanol,2-Ethyl (47) 1.20.5 Undecane,3,8-Dimethyl (43) 3.4 1.4 Undecane,4,6-Dimethyl (59) 16 0.50.2 Nonane,3-methYI-5-propyl (53) 17 0.7 0.3 Nonane,5-Butyl (59) 1 0.4Undecane (90) 1 0.4 Undecane,4-Methyl (72) 1 0.4Benzene,1-Ethyl-2,3-dimethyl (38) 0.5 0.2 Benzene,-4-Ethyl,1,2-dimethyl(72) 0.3 0.1 Dodecane,2,5-Dimethyl (40) 1.1 0.4 Acetophenone (47) 0.70.3 1-Octanol,2-Butyl (78) 0.4 0.2 Benzene,1-Ethyl,2,4-dimethyl (47) 0.30.1 Dodecane,2,7,10-Trimethyl (59) 0.8 0.3 Undecane,2,7,10-Dimethyl (53)0.3 0.1 Benzoic acid (41) 18 8.9 3.6 Dodecane (87) 0.5 0.2 Phenyl maleicanhydride (23) 0.4 0.2 Trimethyl,1,3-Pentadiol diisobutyrate (42) 19 2.91.2 Benzophenone (42) 0.1 0.05 2,5-Cyclohexadiene-1,4-dione-2,5-diphenvl(89) 20 12.1 4.8 Total 216 96

FIGS. 13A and 13B are chromatograms of another gas sample in accordancewith a preferred embodiment of the present invention. The gas sample isa sub-fabricated ambient air sample.

Table 6 lists the mass spectrometry results for oil free air upstream ofthe filter. TABLE 6 Concentration, ug/m3 (as Compound toluene) ashexadecane Silane,Dimethoxydimethyl 0.5 0.2 Toluene 0.3 0.1 Total /0.80.3

FIG. 14 is a graphical illustration of a chromatogram of a sample of oilfree air before a filter in accordance with a preferred embodiment ofthe present invention.

Table 7 lists the mass spectrometry results for oil free air sampleddownstream of the filter. TABLE 7 Concentration, ug/m3 (as Compoundtoluene) as hexadecane Silane,Dimethoxydimethyl 2.3 0.9Silane,Trimethoxymethyl 1.3 0.5 Total 3.6 1.4

FIG. 15 is a graphical illustration of a chromatogram of a sample of oilfree air downstream of the filter in accordance with a preferredembodiment of the present invention.

Table 8 lists the mass spectrometry results for nitrogen facilitiesupstream of the filter. TABLE 8 Concentration, ug/m3 (as Compoundtoluene as hexadecane Silane,Dimethoxydimethyl 0.8 0.3Silane,Trimethoxymethyl 0.3 0.1 Total 1.1 0.4

FIG. 16 is a graphical illustration of a chromatogram of a sample ofnitrogen gas upstream of a filter in accordance with a preferredembodiment of the present invention.

Table 9 lists the mass spectrometry results for nitrogen downstream ofthe filter. TABLE 9 Concentration, ug/m3 (as Compound toluene) ashexadecane Silane,Dimethoxydimethyl 0.9 0.4 Total 0.9 0.4

FIGS. 17A and 17B graphically illustrate a chromatogram of a sample ofnitrogen gas downstream the filter system and an average ion scan of theend of the spectra, respectively, in accordance with a preferredembodiment of the present invention.

FIG. 18 graphically illustrates a chromatogram of a blank sampling tubein accordance with a preferred embodiment of the present invention.

FIG. 19 is a flow chart of a method 600 for on-line monitoring of theperformance of a filter system in accordance with a preferred embodimentof the present invention. The real-time monitoring system for theperformance of the filter system includes taking a sample of theairstream upstream of the filter system per step 602. The spectrum, forexample, a chromatogram of the airstream is generated and stored perstep 604. A threshold target range, in terms of, but not limited to,compounds and quantity, for example, C₅, 32 ppb, is determined. In step606, all contaminants below the target filteration range, location andquantity are identified. In step 608, it is determined if thecontaminants match those present in the upstream sampling location. Ifit is determined that there is no match, then another sample is taken atthe location and the process iterated. However, if the contaminant levelmatches the threshold range upstream of the filter then an alarm is setper step 618, indicating a breakthrough condition for the particularcompound.

Per step 610, for contaminants within the threshold target filtrationrange, location and quantity, for example, C₇, 12 ppb are identifiedfrom the spectrum. The total challenge for each location is updated instep 612 and the remaining filter life is calculated in step 614.

The remaining filter life is compared to a predetermined warning limitin step 616. If the filter life is not greater than the warning limitthen the alarm is set per step 618. However, if the filter life isgreater than the warning limit then the process is iterated again bytaking a sample in step 602 and progressing through the method describedherein.

These steps in accordance with the method are iterated for samples takenat different locations such as, but not limited to, a locationdownstream of the filter, at locations in the filter bed or within aninterstack filter configuration including filter beds in a seriesconfiguration.

The target range in preferred embodiments can include variables such asamplitude of the peaks in a spectrum indicative of the concentration ofthe compounds, or fast moving compounds through the filter systemindicative typically of low molecular weight compounds. In an alternateembodiment a mixture of species may be used as a determinant to monitorfilter life and performance or combinations of variables to analyze theefficacy of the filteration system based on a parametric analysis.

FIG. 20 illustrates a schematic block diagram of a system fordetermining and monitoring contaminants and the performance of a filtersystem in accordance with a preferred embodiment of the presentinvention. The system 650 includes a clean dry air filter 652 upstreamof the system, a base module 654 and a module 682 having a plurality offilters or refractory traps. The base module provides an interface tothe filter module 682 and includes a pressure regulation device 656proximate to the inlet interface 674. The outlet interface 678 is incommunication with the outlet interface of the filter module 682 and theexhaust of the system 672. The exhaust interface 672 can also, inalternate embodiments, be coupled to a vacuum system if evacuation ofthe system for determining contamination is required. All the inlet andoutlet interfaces have sealed surfaces for environmental isolation. Thebase module 654 further includes a controller/processor 658 such as aproportional integral controller and a control module 670 in preferredembodiments. A preferred embodiment includes electronically controlledvalves to impose a duty cycle for sampling per filter cartridge. Theduty cycle can be programmable. The electronically controlled valvesassist in embodiments having high concentrations of impurities as theycan address the potential of overload.

The filter module 682 includes a plurality of filter traps or cartridges686 and an adequate valving arrangement in the interfaces between thecartridges to allow accurate directional flow between filters andpost-collection sampling and analysis at a plurality of sites. Thepost-collection analysis provides quantitative and qualitative measuresof the contamination present in an airstream in the semiconductorprocessing environment. Analysis tools such as, for example, GCMS orGCFID can be used to detect the contaminants. It may also provide formonitoring of the performance of the filter system.

In a preferred embodiment, the filter module can also include a timerdevice, for example, a battery powered clock to determine a samplingduration commensurate with predetermined control parameters. A manifold688 in the filter module provides for flow between the plurality offilters. The manifolds have mechanical interfaces such as adequatebeveling to help in the insertion of the filter cartridges. In apreferred embodiment the channels in the filter module can accommodatefilter blanks or trap blanks which eliminate measurement errors.

In alternate embodiments the analysis system can be cooled using athermoelectric cooling device. Organics can be condensed and collectedusing the low temperature embodiment. A fewer number of traps arerequired for the low temperature embodiment since the organics can becollected post condensation. An embodiment of the low temperature systemcan include heat sinks to dissipate the heat energy generated.

Alternate embodiments include safety devices coupled to externalinterface connections in the event pressure is lost. This obviatessampling inaccuracies.

FIG. 21 illustrates a schematic diagram of the modules in accordancewith a preferred embodiment of the system for detecting and monitoringcontaminants and the performance of a filter system of the presentinvention. A cover 702 is placed over the base module 704 and the filtermodule 706. The filter module 706 includes a plurality of filtercartridges 708 as described with respect to FIG. 20.

FIG. 22 illustrates a schematic diagram of a module having a pluralityof filter traps of the detection system in accordance with a preferredembodiment of the present invention. The base module 704 is illustratedas being coupled to the filter module 706 as discussed with respect toFIG. 20.

FIG. 23 illustrates an alternate view of the module having a pluralityof filter traps as shown in FIG. 21.

FIG. 24 illustrates a detailed view of the module having a plurality offilter traps as shown in FIG. 21 along with the plumbing in themanifolds in accordance with a preferred embodiment of the presentinvention.

FIGS. 25A-25C illustrate schematic diagrams of a device that functionsas a concentrator in a contaminant and filter monitoring system as itincreases the sensitivity of collection in accordance with a preferredembodiment of the present invention. The concentrator device 804 has acover 802 and is inserted in a manifold, for example, manifold 806 thathas the inlet and outlet interfaces. The filter system including afilter monitoring functionality can be reduced in size using a couplingdevice such as, for example, the concentrator 804. A greater volume canbe collected in the filter system if the temperature is reduced, forexample, to 0° C. or below. The sensitivity of data collection is alsoincreased by the use of the concentrator device that includes absorptivematerials such as, for example, Tenax® T.A. High boilers, such as, forexample, organics having six carbon atoms or more are absorbed by Tenax®T.A. In the alternative, absorptive materials such as, for example,carbon traps such as supplied by, for example, Supelco can be used inembodiments including low boilers. Alternate embodiments include acombination of the filters for high and low boilers which can bearranged in parallel and/or in series.

FIGS. 26A and 26B illustrate schematic block diagrams of a system thatemulates and detects a deposition process on optical elements inaccordance with a preferred embodiment of the present invention. Asdescribed hereinbefore, photochemical deposition reactions occur whenhigh-energy photons interact with organic vapors. These reactions formextremely reactive free radicals which may form larger organic compoundscan contaminate optical elements. A polymer layer may be formed on theoptical surfaces and contaminate the optical elements. A preferredembodiment includes a detection system that emulates the depositionprocess of organic compounds on optical surfaces. A filter cartridge 902filled with a glass pack such as, for example, glass beads 912 emulatesthe optical materials. Compressed, clean dry air 910 is passed throughthe filter cartridge. A light source 906 provides light, for example, alaser providing laser light energy to the cartridge to cause theformation of a polymer film on the surfaces of the glass beads as highenergy photons react with organic vapors in the trap.

The photodetector includes a photocell 904 to measure the energy levelof light, which is altered based on the deposition of contaminants onthe surfaces of the multitude of glass beads. The glass beads providefor a larger surface area for deposition. The spectral and transmissiondifferences are monitored to determine the level of contamination. Thisembodiment provides a prospective method to determine damage that canoccur on the optical elements such as, for example, the optics in thestepper. Measures can then be taken to counter the potential damage tovaluable optics.

It should be understood that the programs, processes, methods andsystems described herein are not related or limited to any particulartype of collection media, or computer or network system (hardware orsoftware), unless indicated otherwise. Various types of general purposeor specialized computer systems may be used with or perform operationsin accordance with the teachings described herein.

In view of the wide variety of embodiments to which the principles ofthe present invention can be applied, it should be understood that theillustrated embodiments are exemplary only, and should not be taken aslimiting the scope of the present invention. For example, the steps ofthe flow diagrams may be taken in sequences other than those described,and more or fewer elements may be used in the block diagrams. Whilevarious elements of the preferred embodiments have been described asbeing implemented in software, other embodiments in hardware or firmwareimplementations may be used, and vice-versa.

It will be apparent to those of ordinary skill in the art that methodsinvolved in the system and method for determining and controllingcontamination may be embodied in a computer program product thatincludes a computer usable medium. For example, such a computer usablemedium can include a readable memory device, such as, a hard drivedevice, a CD-ROM, a DVD-ROM, or a computer diskette, having computerreadable program code segments stored thereon. The computer readablemedium can also include a communications or transmission medium, suchas, a bus or a communications link, either optical, wired, or wirelesshaving program code segments carried thereon as digital or analog datasignals.

In another aspect, the present invention provides systems, apparatusesand methods for passive monitoring of contamination in a semiconductorprocessing system using passive samplers and sampling instead of activesampling. As used herein, “active sampling” refers to the use of airmoving device which utilizes an external source of energy coupled to thesampling system to deliver a gas sample to a collection material of acollection device of the sampling system. In comparison, passivesampling uses the energy of the gas sample itself to deliver a gassample to a collection material of a collection device, for example, bydiffusion.

Typically, passive sampling has been considered inadequate formonitoring contamination in a semiconductor processing system because ofthe generally very low sample delivery rates associated with passivesampling. For example, for a system which may have a sample deliveryrate of 0.1 liters/min. with active sampling, can have a sample deliveryrate of only 0.0001 to 0.001 liters/min. In another example, for activesampling using a hand held pump to pull air through a Tenax® TA tube ata flow rate of 0.150 liters/min., the diffusive flow rate is 0.0003liters/min for passive sampling. As a result, passive sampling at a flowrate of 0.0003 liters/min. typically needs to be conducted for over 83days to achieve the same total sampling volume of active sampling at aflow rate of 0.150 liters/min for 4 hours. Accordingly, passive samplinghas generally been viewed as inadequate for monitoring tracecontaminants (for example, contaminants with a concentration less thanabout 10 ppb) because of the long sampling duration needed to sample avolume of contaminant comparable to that collected by active sampling.

Active sampling, however, has several disadvantages. Active samplingrequires an external source of energy for the active sampling system,which may limit the number and placement of such active systems in, forexample, a semiconductor processing facility or system. In addition, byrequiring a source of power active systems are susceptible to failuredue to power outages or breakdown of the external source of energy, suchas, for example, a pump. In comparison, a passive sampling system, inaccordance with a preferred embodiment of the present invention, istypically unaffected by power outages and there is no external source ofenergy for the sampling system which can breakdown.

Other disadvantages of typical prior art active sampling approaches,which use a pump as an active source of energy, include, for example:calibration of multiple devices (such as, for example, the pump, flowmeters, and timers); pump vibration; and the need for trained systemoperators.

In comparison, in a passive sampling system, in accordance with apreferred embodiment of the present invention, only one parameter, theflow rate, is calibrated. In another embodiment, of the presentinvention, a sampling duration time is calibrated, but no flowparameters are calibrated. In addition, in accordance with a preferredembodiment of the passive sampling system of the present invention, thepassive system substantially operates on its own without the need forconstant operator oversight.

In one aspect, the present invention provides passive sampling systemsfor monitoring contaminants in a semiconductor processing system.Referring to FIG. 27, in one embodiment, that passive sampling system2700, comprises a collection device 2701 in fluid communication with asample line 2705 which in turn is in fluid communication with asemiconductor processing system 2703. A flow regulator 2707 can bedisposed in the sample line 2705 to regulate a flow of gas 2709 out ofthe semiconductor processing system 2703. In one embodiment, thesemiconductor processing system comprises a photolithography instrument.The flow of gas 2709 can arise for example, from semiconductorprocessing system over pressure.

In accordance with a preferred embodiment, the semiconductor processingsystem comprises a photolithography cluster tool, such as for example,an exposure tool, used in manufacturing semiconductor devices, that issensitive to molecular contamination and a filtering system whichremoves the molecular contamination which may include volatile andsemi-volatile or condensable organic substances, which, if present, cancause contamination of optical elements via series of homogeneous and/orheterogeneous ultraviolet (UV) induced processes.

The collection device 2701 contains an absorptive material 2711 tocollect one or more contaminants from the flow of gas 2709. Thecollection device 2701 is sealed at the end distal 2713 to the sampleline 2705. The proximal end 2715 of the collection device 2701 is influid communication with the sample line 2705 such that the absorptivematerial 2711 is capable of receiving one or more contaminants from theflow of gas 2709 by a passive transport process, such as, for example,diffusion. In a preferred embodiment, one or more contaminants reach theabsorptive material substantially by diffusion from the flow of gas. Forexample, in one embodiment, the collection device comprises a ¼″diameter by 3″ long Tenax®) tube, which is connected to he sample lineby a Swagelok® fitting. The ¼″ diameter by 31/2″ long Tenax® tubecontains about 150 milligrams (mg) of adsorptive material.

In accordance with preferred embodiments, the collection device 2701includes an amount of adsorptive material with an adsorption capacityequivalent to an amount of Tenax T.A. in the range from about 0.05 g toabout 1.0 g.

In another embodiment, the sample line is positioned such that the flowof gas comprises gas from a location downstream of a filter or filtersystem. In another embodiment, the sample line is positioned such thatthe flow of gas comprises gas from a location upstream of a filter orfilter system. In another embodiment, the sample line is positioned suchthat the flow of gas comprises gas from a location inside a filter orfilter system. In one version of these embodiments, the passive samplingsystem is configured to monitor the condition of the filter or filtersystem. For example, the passive sampling system, which can comprise oneor more collection devices, sampling lines etc., can be configured tosample a gas flow from a location upstream and a location downstream ofa filter to assess breakthrough of a target contaminant.

In various embodiments, the passive sampling systems of the presentinvention further comprise a monitor system 2717 positioned to measurethe temperature, the pressure, or both, of the flow of gas. Preferably,the monitor system 2717 measures the temperature and pressure of aregion adjacent the proximal end 2715 of the collection device 2701. Inone embodiment, the monitor system 2717 measures the temperature andpressure of a region adjacent to the flow regulator 2707, inside theflow regulator 2707, or both.

In various embodiments, the passive sampling systems of the presentinvention further comprise a regulator system 2721 positioned toregulate the temperature, the pressure, or both, of the flow of gas.Preferably, the regulator system 2721 regulates the temperature, thepressure, or both, of the flow of gas at least in a region adjacent theproximal end 2715 of the collection device 2701. In one embodiment, theregulator system 2721 regulates the temperature and pressure of a regionadjacent to the flow regulator 2707, inside the flow regulator 2707, orboth.

The regulator system 2721 can comprise, for example, a heating/coolingdevice 2123 proximate to or in contact with, for example, the sampleline 2705. Examples, of suitable heating/cooling devices include, butare not limited to, thermoelectric devices.

In various embodiments, the regulator system regulates temperature,pressure, or both, based at least in part on measurements provided by amonitoring system. For example, a regulator system 2721 can send asignal to a heating/cooling device 2123 based on a temperature measuredby the monitor system 2717 to bring the temperature of the gas flow in aregion of the sample line 2705 into a selected temperature range. Inaddition, the regulator system 2721 can send a signal to a flowregulator 2707 (such as, for example, a mass flow controller) based on apressure measured by the monitor system 2717 to bring the pressure ofthe gas flow in a region of the sample line 2705 into a selectedpressure range.

In various embodiments, the passive sampling systems of the presentinvention further comprise a backflow prevention device 2725 positionedin the sample line 2705 such that it is capable of substantiallypreventing gas flow from the sample line 2705 into the semiconductorprocessing system 2703. Preferably, the backflow prevention device 2725comprises a filter positioned in the sample line such that it is capableof substantially preventing gas flow from the sample line into thesemiconductor processing system. Examples of suitable backflowprevention devices include, but are not limited to, checkvalves with orwithout activated filter is in series.

The collection device includes absorptive material such as, for example,a refractory absorptive material. In one embodiment, glass spheres of agiven size are used. In a preferred embodiment, crushed glass spheresare used. In another preferred embodiment, the absorptive material isthe polymer Tenax®. For example, Tenax®. has a high capacity for highboiling point compounds and operating Tenax®. past low molecular weightbreakthrough capacity allows the capture of high molecular weightcompounds. Preferably, the absorptive material of the collection deviceis a material capable of collecting one or more contaminants in amolecular weight range of interest. In a preferred embodiment, theabsorptive material is capable of collecting C₆-C₃₀ containingcontaminants. In another embodiment, the absorptive material is capableof collecting molecular bases or/and molecular acids, and comprises, forexample, a reagent treated glass fiber non-woven media.

The sample line may comprise any material suitable for conveying a gasflow from the semiconductor processing system. Suitable materials can beselected, for example, based on the known or predicted reactivity of thesample line material with known or suspected constituents in the gasflow. Suitable materials include, but are limited to, PFA, stainlesssteel, Ni, quartz, polytetrafluoroethylene (PTFE). Preferably, thesample line comprises a PFA tube.

It is further preferred that the internal surface of the sample line, atleast in the portion between the semiconductor processing system and thecollection device, is equilibrated with the flow of gas. The internalsurface of the sampling line is preferably in equilibrium with the gasphase sample in order to not interfere with the contaminant collectionprocess. For example, it is preferred that the concentration ofcontaminants of interest on an internal surface of the sample line aresuch that the internal surface of the sample line does not significantlyuptake the contaminants of interest from the flow of gas. A sample linemay be equilibrated, for example, by inputting a gas flow until theconcentrations of one or more contaminants of interest at the input tothe sample line are substantially the same as the concentrations at theoutput of the sample line. In another example, an approximately twentyfoot long sampling line was found to be substantially equilibrated withhexadecane contaminants in typical clean room air after approximately24-48 hours using a gas flow rate of 0.15 liter/min. of the clean roomair. Although sample line equilibration tests were conducted with anapproximately twenty foot line, it is preferred that the sampling linebe as short as possible. In practical applications, it is believed thatsample lines in the range from about one to five feet may be practicaland will have correspondingly shorter equilibration times than a twentyfoot line.

In addition, it is preferred that in operation the absorptive materialof the passive sampling systems of the present invention is exposed to asubstantially continual flow of gas from the semiconductor processingsystem such that the collection device samples a fresh sample of thegas. In one embodiment, the gas flow rate is in the range from about 0.3liters/min. to about 3 liters/min. In a preferred embodiment, the gasflow rate is greater than about 1 liter/min.

The flow regulator may be any device or structure suitable forregulating the flow of gas from the semiconductor processing system. Forexample, the flow regulator can be a valve, a series of valves, acritical orifice or series of critical orifices, a voltage sensitiveorifice or series of voltage sensitive orifices, a mass flow controller(MFC), a temperature regulated flow controller, or combinations thereof.In a preferred embodiment, the flow regulator is adapted to regulate theflow of gas to a flow rate in the range from about 0.3 liters/min. toabout 5 liters/min.

In another aspect, the present invention provides passive samplingapparatus for monitoring contaminants in a semiconductor processingsystem. In one embodiment, referring to FIG. 27, the apparatus comprisesa sample line 2705 having a portion 2730 adapted to be placed into fluidcommunication with a semiconductor processing system.

In accordance with a preferred embodiment, the adapted portion 2730 ofthe sample line is adapted to be placed into fluid communication withthe semiconductor processing system comprising a photolithographycluster tool, such as for example an exposure tool, used inmanufacturing semiconductor devices, that is sensitive to molecularcontamination and a filtering system which removes the molecularcontamination which may include volatile and semi-volatile orcondensable organic substances, and/or inorganic compounds, which, ifpresent, can cause contamination of optical elements via series ofhomogeneous and/or heterogeneous ultraviolet (UV) induced processes.

Suitable sample lines, collection devices, absorptive materials, flowregulators, backflow prevention devices, monitor systems, and regulatorsystems, for the passive sampling apparatuses of the present invention,include, but are not limited to, those discussed in the context of FIG.27 and the passive sampling systems for monitoring contaminants in asemiconductor processing system of the present invention.

In another aspect, the present invention provides methods for passivemonitoring of contaminants in a semiconductor processing system. In oneembodiment, the method monitors contaminants in a filter or filtersystem of a semiconductor processing system.

Referring to FIG. 28, various embodiments of methods for passivemonitoring of contaminants in a semiconductor processing system 2800 areshown. The methods provide a collection device containing an absorptivematerial 2810. Suitable collection devices and absorptive materials forthe methods of the present invention include, but are not limited to,those discussed in the context of the passive sampling systems formonitoring contaminants in a semiconductor processing system. Themethods proceed with sampling one or more contaminants by diffusion ofthe contaminants to the collection device 2820 from a gas or gas flow,and at least a portion of these contaminants are collected by theabsorptive material 2830. In a preferred embodiment, one or morecontaminants reach the absorptive material substantially by diffusionfrom the flow of gas. An appropriate analytical technique is then usedto identify at least one of the contaminants collected by the absorptivematerial 2840.

In preferred embodiments of the methods for passive monitoring ofcontaminants in a semiconductor processing system of the presentinvention, the collection device is exposed to a substantially continualsupply of gas to be sampled during the step of sampling 2820 and,preferably, during the step of collecting 2830. In various embodiments,the collection device is exposed to a substantially continual flow ofgas from the semiconductor processing system such that the collectiondevice samples a fresh sample of the gas. In other embodiments, thecollection device is placed inside the semiconductor processing systemand exposed to a substantially continual flow of gas through thesemiconductor processing system such that the collection device samplesa fresh sample of the gas. In one embodiment, the gas flow rate is inthe range from about 0.3 liters/min. to about 3 liters/min. In apreferred embodiment, the gas flow rate is greater than about 1liter/min.

The provision of a fresh sample allows the absorptive material tocollect a greater contaminant sample volume in a given time period, forexample, by maintaining a contaminant concentration gradient between asampling volume (for example, a volume of gas in a sample line or volumeof gas in a semiconductor processing system) and the volume adjacent theabsorptive material of the collection device. It is to be understoodthat the concentration gradient drives, in part, the rate of first orderdiffusion of a gas.

In various embodiments, the methods for passive monitoring ofcontaminants in a semiconductor processing system of the presentinvention further comprise a step of providing a sample line having aportion adapted to be placed into fluid communication with thesemiconductor processing system. In these embodiments, it is preferredthat the methods for passive monitoring of contaminants in asemiconductor processing system further comprise a step of conditioningthe sample line to equilibrate the internal surface of the sample line,at least in the portion between the semiconductor processing system andthe collection device, with the flow of gas. The internal surface of thesampling line is preferably in equilibrium with the gas phase sample inorder to not interfere with the contaminant collection process.

For example, it is preferred that the concentration of contaminants ofinterest on an internal surface of the sample line are such that theinternal surface of the sample line does not significantly uptake thecontaminants of interest from the flow of gas. A sample line may beequilibrated, for example, by inputting a gas flow until theconcentrations of one or more contaminants of interest at the input tothe sample line are substantially the same as the concentrations at theoutput of the sample line. In another example, an approximately twentyfoot long sampling line was found to be substantially equilibrated withtypical organic contaminants in typical clean room air afterapproximately 24 hours using a gas flow rate of 1 liter/min. of theclean room air.

In one embodiment, the method samples by diffusion 2820, from a gas flowto a collection device, one or more contaminants in the gas flow; and atleast a portion of these sampled contaminants are collected by theabsorptive material 2830 of the collection device. Structures,collection devices, and absorptive materials suitable for sampling andcollecting in accordance with these embodiments of the present inventioninclude, but are not limited to, those discussed in the context of FIG.27.

In another embodiment, the method samples by diffusion 2820, from a gasin the semiconductor processing system to an adsorptive material of acollection device, one or more contaminants; and at least a portion ofthese contaminants are collected by the absorptive material 2830.Collection devices and absorptive materials suitable for sampling andcollecting in accordance with these embodiments of the present inventioninclude, but are not limited to, those discussed in the context of FIG.27. In one embodiment, the collection device has a shape adapted to beplaced into a semiconductor wafer carrier. For example, the collectiondevice can comprise a 200-300 mm diameter thick wafer with absorptivematerial disposed (for example, deposited, or grown) on one or bothsides of the wafer. This wafer collection device can then be placed intoa semiconductor processing system, together with actual semiconductorwafers or by itself, to provide an in situ monitor of contaminants inthe semiconductor processing system. In another embodiment, thecollection device or at least a portion of the absorptive material ispositioned in the semiconductor processing system through a port in theprocessing system.

In various embodiments, the step of sampling contaminants 2820 comprisessampling for a sample duration. The sample duration can be chosen, forexample, based on required lower detection limit of the procedure. Inone embodiment, the sample duration is chosen such that a contaminantwith an uptake rate of 1.5 ng per ppb per minute on the absorptivematerial is detectable, to a selected degree of uncertainty, by theanalyzer technique and instrumentation employed in identifying thecontaminant. In another embodiment, the sample duration is chose suchthat a contaminant with an uptake rate in the range from about 1.9 toabout 4.2 ng per ppb per minute on the absorptive material isdetectable, to a selected degree of uncertainty, by the analyzertechnique and instrumentation employed in identifying the contaminant.

In a preferred embodiment, the analyzer comprises a mass spectrometryinstrument, which is tuned to transmit only a single narrowmass-to-charge ratio range of interest to increase detection sensitivityand thereby decrease the sample duration required to detect acontaminant of interest to a selected degree of uncertainty. Preferably,the sample duration is in the range from about 5 min to about 50 min foran aromatic contaminant, such as, for example, toluene with an uptakerate of 1.9-4.2 ng/ppb/min and an adsorptive material with a surfacearea in the range from about 620 cm² to about 1440 cm² using a GCMSinstrument to identify the toluene contaminant, where the massspectrometer is tuned to transmit ions with a mass-to-charge ratio inthe range from about 91 to about 93. In another embodiment, for example,using a ¼″ Tenax®. tube and a gas flow rate in the range from about 0.3liters/min. to about 3 liters/min, the sample duration is in the rangefrom about 2 months to about 4 months.

Preferably, the analyzer uses a detection technology that is inherentlysensitive to, and can identify and quantify organic species at very lowconcentrations, for example, below 1 ppb (V). Suitable approaches fordetecting contaminants using a analyzer 2840 include, for example, gaschromatograph/flame ionization detection (GCFID), and combinationchromatography-mass spectrometry techniques and instrumentation. Theanalyzer may include any system that is capable of measuring organiccompounds at very low concentrations including, but not limited to aGCFID with, or without a preconcentrator, a gas chromatography-massspectrometry (GCMS) with, or without a preconcentrator, a photoacousticdetector with, or without a preconcentrator, and TMS with, or without apreconcentrator, or any combination thereof.

Combination chromatography-mass spectrometry techniques andinstrumentation include, but are not limited to, gas chromatography-massspectrometry (GCMS), liquid chromatography-mass spectrometry, and highperformance liquid chromatography-mass spectrometry (HPLC-MS). Inaddition, techniques, such as tuning the mass spectrometry instrument totransmit only a narrow mass-to-charge ratio range of interest, can beused to increase detection sensitivity. For example, for a typicalradio-frequency multipole mass spectrometer, the signal-to-noise (SN)for a given charge-to-mass ration is proportional to the square root ofthe time the mass spectrometer is transmitting that mass-to-chargeratio. As a result, tuning a mass spectrometer to transmit only a narrowmass-to-charge ratio range can improve, in some cases, the SN for thatratio range by two orders of magnitude versus broader scanning of themass spectrometer.

In a preferred embodiment, analyses of molecular bases and molecularacids samples includes using ion chromatography methods. Contaminantsare identified by retention time and quantified using, for example,individual calibration standards and a 10-point calibration procedure.The Low Detection Limit (LDL) of these chromatographic methods isapproximately 0.1 ug/m³ per individual component. In a preferredembodiment, molecular bases and refractory material samples are analyzedusing a gas chromatograph (GC) equipped with a mass selective detector(such as, for example, a mass spectrometer) and Thermal DesorptionSystem (TD). The total analytical system (TD/GC/MS) is optimized toseparate and quantify analytes with a boiling temperature of hexane andhigher with LDL of approximately 0.1 ug/m³ per individual component.Individual components, and thereby contaminants, are identified by amass spectrometry library search and chromatographic peak position. Inone embodiment, contaminant concentrations are quantified against twoanalytical standards, for example, toluene and hexadecane.

It is to be understood that techniques and instrumentation can be chosenbased on the semiconductor processing system and process to which themethods of the present invention are applied. For example, in oneembodiment of passive monitoring of contaminants in a filter or filtersystem, the step of identifying targets a low boiling point contaminantpropagated through the filter. This targeted contaminant can serve, forexample, as a leading indicator gas. In these embodiments, the analyzertechniques and instrumentation need only be capable of identifying thetarget contaminant.

In other embodiments, identification of a range of contaminant masses isdesired. For example, in monitoring first, second, third, and fourthorder contamination effects in a photolithography tool, the targetcontaminants can comprise high molecular weight refractory organics andcompounds including carbon atoms within the range of approximately oneto thirty carbon atoms C₁-C₃₀. The first order contaminants may comprisehigh molecular weight refractory organics such as, for example, C₆siloxanes and C₆ iodide with an inorganic component which is notvolatilized through combination with oxygen. Second order contaminantsmay comprise high molecular weight organics, such as, for example,compounds including carbon atoms within the range of approximately sixto thirty carbon atoms (C₆-C₃₀). Third order effects can arise due tothe contaminating effects of organics such as C₃-C₆ that haveapproximately three to six carbon atoms. Fourth order contaminantsinclude organics such as, for example, methane, that have approximatelyone~to five carbon atoms.

In other embodiments, target contaminants can comprise only first andsecond order contaminants because first and second order contaminatingeffects have a greater impact on the contamination of optical systemsthan third or fourth order contaminants. In these embodiments, theanalyzer techniques and instrumentation need only be capable ofidentifying these target contaminants.

Referring again to FIG. 28, in various embodiments, the methods forpassive monitoring of contaminants in a semiconductor processing systemof the present invention further comprise a step of evaluating thecondition of a filter 2850 of the semiconductor processing system basedat least in part on one or more contaminants identified by the analyzer.The filter may be a single filter, multiple filters or a filter system.In one embodiment, the step of evaluating evaluates the condition of afilter based on the concentration of a low boiling point targetcontaminant propagated through the filter. This targeted contaminant canserve, for example, as a leading indicator gas. Preferably, the targetedcontaminant travels faster in the filter than other target contaminants.These methods including a step of evaluating preferably establish acorrelation between one or more low molecular weight compounds and oneor more high molecular weight compounds to determine the condition ofthe filter with respect to a one or more contaminants of interest.

Further, the methods for passive monitoring of contaminants in asemiconductor processing system including a step of evaluating thecondition of a filter preferably include sampling a gas flow at amultiple locations, such as, for example, upstream, downstream andinside of the filter.

In one embodiment, the methods for passive monitoring of contaminants ina semiconductor processing system of the present invention furthercomprise a step of measuring at least one of temperature, pressure orflow rate of a gas flow 2860. In another embodiment, the methods forpassive monitoring of contaminants in a semiconductor processing systemof the present invention further comprise a step of monitoring at leastone of temperature and pressure of a gas in the semiconductor processingsystem 2860. These measurements can be used to provide increasedaccuracy in the quantitative determination of one or more contaminantconcentrations in the semiconductor processing system. For example, anaverage contaminant concentration in a semiconductor processing systemcan be determined from a contaminant concentration determined in theidentifying step using the gas flow rate, temperature and pressure,assuming a sufficiently equilibrated sampling line. In addition, thetemperature, pressure and flow rate measurements can be used inembodiments comprising a step of evaluating the condition of a filter toevaluate the condition of a filter or filter system.

Structures and monitor systems suitable for the step of measuringinclude, but are not limited to, those discussed in the context of FIG.27. Preferably, the step of measuring 2860 measures the temperature,pressure, and flow rate in a region adjacent the proximal end of thecollection device. In one embodiment, the step of measuring 2860measures the temperature, pressure and flow rate in a region adjacent toa flow regulator, inside the flow regulator, or both.

In one embodiment, the methods for passive monitoring of contaminants ina semiconductor processing system of the present invention furthercomprise a step of regulating at least one of temperature, pressure orflow rate of a gas flow 2870. In another embodiment, the methods forpassive monitoring of contaminants in a semiconductor processing systemof the present invention further comprise a step of regulating at leastone of temperature, pressure of a gas in the semiconductor processingsystem 2870. In various embodiments, the step of regulating regulatestemperature, pressure, or both, based at least in part on measurementsprovided by a monitoring system.

The step of regulating can be used to provide increased accuracy in thequantitative determination of one or more contaminant concentrations inthe semiconductor processing system. Structures and regulator systemssuitable for the step of regulating include, but are not limited to,those discussed in the context of FIG. 27. Preferably, the step ofregulating 2860 regulates the temperature, the pressure, or both, of theflow of gas at least in a region adjacent the proximal end of acollection device. In one embodiment, the step of regulating 2860regulates the temperature and pressure of a region adjacent to a flowregulator, inside the flow regulator, or both.

In another aspect, the present invention provides systems and methodsfor detecting airstream backflow in a semiconductor processing systemusing a differential pressure monitor.

In semiconductor processing, the direction of airstream flow can becritical to controlling system contamination. One area of particularconcern is the backflow of an airstream from the track into the stepper.Typically, the airstream flows from the stepper to the track. In certainsituations, however, this airstream may be misdirected causing air tobackflow into the stepper. Such misdirection can occur, for example,when a processing tool is stopped, a processing tool door is opened, ora system air filter fails.

Misdirected airstream flow can have serious consequences. For example,during backflow -contaminants in the track can be forced into thestepper and potentially onto to the optics of the photolithography toolsconnected to the stepper.

In one aspect, the present invention provides a system for detectingairstream backflow using a differential pressure monitor. In preferredembodiments, the present invention provides a system for detectingbackflow from the track into the stepper. Referring to FIG. 29A, thesystem detects backflow in a semiconductor processing system comprisingan airstream source 2901 (such as, for example, a track) and a deliveryregion 2903 (such as, for example, a stepper). The system comprises adifferential pressure monitor 2905 comprising a first pressuremeasurement device 2907 positioned at the airstream source 2901, and asecond pressure measurement device 2909 positioned at the deliveryregion 2903. In desired operation of the semiconductor processingsystem, the pressure, P.sub.1, in the source airstream 2901 is greaterthan in the pressure, P.sub.2, in the delivery region 2903; and theairstream 2911 flows from the source 2901 to the delivery region 2903.This situation is illustrated in FIG. 29A.

The differential pressure monitor 2905 monitors the difference inpressure between the pressure, P₁, in the source airstream 2901 and thepressure, P₂, in the delivery region 2903. When P₁ is greater than P₂,the differential pressure monitor 2905 provides, for example, no signal,or a signal indicating normal airflow.

When the pressure, P₂, in the delivery region 2903 is greater than thepressure, P₁, in the source airstream 2901, conditions may exist forairstream backflow 2915. This situation is illustrated in FIG. 29B. Whenthe differential pressure monitor 2905 detects that P₂ is greater thanP₁, the differential pressure monitor 2905 provides a warning signalindicating potential backflow in the semiconductor processing system.

FIGS. 30A-30E illustrate schematic diagrams of another embodiment of adevice that can function as a concentrator in a contaminant and filtermonitoring system in accordance with a preferred embodiment of thepresent invention. FIG. 30A is an illustration of one embodiment of theconcentrator device 3050, with a cover 3026 in place, and showing oneembodiment of an inlet interface 3054 and an outlet interface 3056. FIG.30B is an exploded assembly drawing of a concentrator 3057, FIG. 30C isan assembly drawing of a concentrator device 3050, and FIG. 30D is anassembly drawing of the concentrator 3057 inserted into a manifold 3059having an inlet interface 3054 and an outlet interface 3056 where, inone embodiment, the components and mounting hardware of FIGS. 30B-30Dare as follows:

-   4-40×¼″ Phillips Head Screw 3001;-   ¼″ Comp. Teflon Elbow Union 3002;-   ⅛″ SS Tubing 3003 (FIG. 30E is a scale drawing of one embodiment of    a ⅛″ SS Tubing 3003);-   ¼″38 ×¼″ Straight Teflon Union 3006;-   ¼″ FPT −¼″ Comp. Stainless Steel (SS) Adapter 3007;-   ⅛″ FPT .times.⅛″ Comp. SS Elbow 3008;-   25 Micron Particle Filter 3009;-   ⅛″ NPT Male 2E Orifice 3010;-   ⅛″ SS Comp. Tee 3011;-   ¼″ Teflon Tubing 3012;-   ¼″ Teflon Comp. Tee 3013;-   Rubber Multi-Tube Holder 3014;-   Refractory Trap Tube Holder Plate 3015;-   6-32×¼″ Phillips Screws 3016;-   ¼″×⅛″ SS Bulkhead Union 3019;-   6-32×¼″ Button Head Screw 3021;-   Locking Plate for Bulkhead 3023;-   ¼″×¼″ SS Bulkhead Union 3024;-   Bulkhead 3025;-   Cover 3026;-   ¼″×3½″ Tenax Tube containing about 150 mg of adsorptive material    3027;-   ⅛″ Teflon Tubing 3028; and-   ¼″ SS Comp. Tee 3029.

The filter system including a filter monitoring functionality can bereduced in size using a device such as, for example, the concentrator3057. A greater volume of contaminants can be collected in the filtersystem over an interval of time if the temperature is reduced to, forexample, 0° C. or lower. Using a concentrator device that includesabsorptive materials such as, for example, Tenax® T.A, in a collectiondevice 3027 can also increase the volume of material collected. Highboilers (compounds with boiling points greater than about 150° C.), suchas, for example, organics having or more six carbon atoms are generallyabsorbed by Tenax® T.A. Preferably, the total mass of adsorptivematerials, such as, for example, Tenax® T.A. is greater than about 0.05grams (g). In another embodiment, the total mass of adsorptive materialis in the range from about 0.05 g to about 1 g.

In another embodiment, absorptive materials for use in the collectiondevice 3027 include, for example, carbon traps such as supplied by, forexample, Supelco can be used in embodiments including low boilers. Otherembodiments include a combination of the collection devices 3027 forhigh and low boilers, which can be arranged in parallel and/or inseries. In addition, the collection device 3027 can be a single deviceinstead of multiple devices arranged in parallel and/or series.

In preferred embodiments, the concentrator 3057 includes two series ofcollection devices 3027 in parallel. A series of collection devicesenables one to better resolve differences in contaminant uptake along alength of adsorption material because the collection devicecorresponding to a given location along the length of adsorptivematerial can be analyzed separately from the others. In comparison, suchresolution is lost when a single collection device, of equal length tothe series, is used because length dependence information is lost due tocontaminants desorbing from the single collection device independent oftheir position along the length of adsorptive material.

Having two substantially identical series of collection devices inparallel is preferred because the redundancy inherent in thisconfiguration increases the reliability of the contaminant analysis byproviding a measure of the variation in collection properties betweencollection devices and provide a measure of variance for the data. Anexample of one preferred embodiment of two substantially identicalseries of collection devices 3027 in parallel is illustrated in FIGS.303B and 30D.

FIGS. 31A-31E illustrate a schematic diagram of a system for monitoringcontaminants and the performance of a filter system in accordance with avarious embodiments of the present invention. In various embodiments,the system 3100 includes a plurality of concentrator devices 3110 (suchas, for example, illustrated in FIGS. 25A-25C and/ or 30A-30E) formonitoring contaminants and the performance of a filter system. Thefilter system includes an inlet interface 3120, a filter module 3140having a plurality of filters 3192 (schematically illustrated in FIG.31E), a HEPA filter module 3150 having a HEPA filter, an outputinterface 3130, and a compressed air inlet 3172 for actuation of systempneumatics. The outlet interface 3130 can also, in other embodiments, becoupled to a vacuum system if evacuation of the system for determiningcontamination is required. The inlet and outlet interfaces preferablyhave sealed surfaces for environmental isolation.

The system 3100 includes interstack sampling ports 3162, 3164, 3166 forsampling the gas stream between filters 3192 or after the filters 3192.The system also includes an inlet sample port 3168 for sampling theinput gas stream prior to filtration and an outlet sample port 3170 forsampling the gas stream after the HEPA filter module 3150 but prior toreturn through the output interface 3130. Preferably, the system alsoincludes a pressure regulation device proximate to the inlet interface3120 and a pressure gauge 3180 to measure pressure in the system.

In one embodiment, the filter module 3140 includes an adequate valvingarrangement to allow accurate sampling of the various sampling ports3162, 3164, 3166, 3168, 3170 by the concentrator devices 3110. A singleconcentrator device 3110 or multiple concentrator devices 3110 can beused to monitor the output of a sampling port and collect a sample forpost-collection analysis. For example, in one embodiment, oneconcentrator device 3110 is connected to each of the five samplingports. In another embodiment, multiple concentrator devices 3110 can beconnected to a single sampling port, for example, where contaminationconcentration is anticipated to be low, such as at the outlet samplingport 3170.

The system can further include a controller/processor, such as aproportional integral controller and a- control module, A preferredembodiment includes electronically controlled valves to impose a dutycycle for sampling per concentrator device. The duty cycle can beprogrammable. The electronically controlled valves can assist inembodiments having high concentrations of impurities as they can addressthe potential of overload. Preferably, the controlled valves arepneumatically actuated with compressed clean dry air.

The post-collection analysis of the material collected by a concentratordevice can provide quantitative and qualitative measures of thecontamination present in a gas stream in the semiconductor processingenvironment. Analysis tools such as, for example, GCMS or GCFID can beused to detect the contaminants. It may also provide for monitoring ofthe performance of the filter system.

In some embodiments the concentrator devices can be cooled using athermoelectric cooling device. Organics can be more readily condensedand collected using the low temperature embodiment. A fewer number oftraps are required for the low temperature embodiment since the organicscan be collected post condensation. An embodiment of the low temperaturesystem can further include heat sinks to dissipate the heat energygenerated.

The claims should not be read as limited to the described order orelements unless stated to that effect. Therefore, all embodiments thatcome within the scope and spirit of the following claims and equivalentsthereto are claimed as the invention.

1. A method for sampling a contaminant in a semiconductor processingsystem, comprising the steps of: delivering a gas stream from thesemiconductor processing system to a collection device, the processingsystem having an optical system; and collecting a contaminant from thegas stream in the collection device for a duration exceeding asaturation capacity of the collection device.
 2. The method of claim 1further comprising determining a contaminant concentration in thesemiconductor processing system from a sample collected with thecollection device.
 3. The method of claim 1 further comprisingcollecting a sample from a photolithography tool.
 4. The method of claim1 further comprising collecting a lower molecular weight contaminant anda higher molecular weight contaminant and continuing to collect thehigher molecular weight contaminant the saturation capacity for thelower molecular weight contaminant.
 5. The method of claim 1 furthercomprising collecting a sample in the collection device with anadsorptive material.
 6. The method of claim 5 further comprisingproviding an adsorptive material including Tenax.
 7. A method formonitoring and removing a contaminant in a photolithography systemhaving an optical path, comprising the steps of: delivering a gas streamfrom a photolithography system to a collection device; collecting acontaminant from the gas stream with the collection device; analyzing acollected sample of the contaminant; and actuating a membrane to removethe contaminant from the optical path.
 8. The method of claim 7, whereincollecting a contaminant comprises collecting at least one of refractorycompounds, high molecular weight compounds and low molecular weightcompounds.
 9. The method of claim 7 further comprising collecting a lowmolecular weight compound and a high molecular weight compound past asaturation capacity of the device.
 10. The method of claim 7 furthercomprising analyzing the collected sample to determine a contaminantconcentrate.
 11. The method of claim 7 further comprising flowing thegas stream through a contaminant removal device including the membrane.12. A method for cleaning a contaminated surface in a semiconductorprocessing system, comprising the steps of: delivering a gas stream tothe contaminated surface in the processing system in the presence oflight, the gas stream having an additive gas and the gas streamcombining with a contaminant on the contaminated surface to form avolatile product; and removing the volatile product from the processingsystem.
 13. The method for cleaning of claim 12, wherein the step ofremoving the volatile product includes using a purge gas.
 14. The methodof cleaning of claim 12, wherein steps of delivering a gas stream to thecontaminated surface further comprises delivering a gas stream to anoptical system surface.
 15. The method of claim 13 wherein the step ofremoving further comprising filtering the volatile product from the gasstream with a filter.
 16. The method of claim 13 further comprisingmonitoring a concentration of the volatile product.
 17. The method ofclaim 12 further comprising removing the volatile product from aphotolithography tool.
 18. The method of claim 12 further comprisingremoving an organic compound.
 19. The method of claim 12 furthercomprising removing an inorganic compound.
 20. The method of claim 12further comprising removing a refractory compound.